Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $223.81   4.540%   $233.971   $233.97   $233.95   $234.00  
  Purchase #2 $82.69   11.487%   $92.1886   $92.19   $92.20   $92.20  
  Purchase #3 $169.98   12.815%   $191.7629   $191.76   $191.75   $191.80  
  Purchase #4 $245.86   12.570%   $276.7646   $276.76   $276.75   $276.80  
  Purchase #5 $165.25   7.515%   $177.6685   $177.67   $177.65   $177.70  
  Purchase #6 $240.35   13.261%   $272.2228   $272.22   $272.20   $272.20  
  Purchase #7 $127.51   11.268%   $141.8778   $141.88   $141.90   $141.90  
  7 purchase totals = $1,255.45       $1,386.4562   $1,386.45   $1,386.40   $1,386.60