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 $194.33   7.509%   $208.9222   $208.92   $208.90   $208.90  
  Purchase #2 $116.63   5.594%   $123.1543   $123.15   $123.15   $123.20  
  Purchase #3 $37.46   4.542%   $39.1614   $39.16   $39.15   $39.20  
  Purchase #4 $152.86   12.833%   $172.4765   $172.48   $172.50   $172.50  
  Purchase #5 $81.67   7.755%   $88.0035   $88.00   $88.00   $88.00  
  Purchase #6 $247.41   11.811%   $276.6316   $276.63   $276.65   $276.60  
  Purchase #7 $129.79   11.469%   $144.6756   $144.68   $144.70   $144.70  
  7 purchase totals = $960.15       $1,053.0251   $1,053.02   $1,053.05   $1,053.10