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 $195.59   12.597%   $220.2285   $220.23   $220.25   $220.20  
  Purchase #2 $150.55   12.335%   $169.1203   $169.12   $169.10   $169.10  
  Purchase #3 $68.89   7.542%   $74.0857   $74.09   $74.10   $74.10  
  Purchase #4 $234.97   6.446%   $250.1162   $250.12   $250.10   $250.10  
  Purchase #5 $79.25   3.742%   $82.2155   $82.22   $82.20   $82.20  
  Purchase #6 $85.66   6.642%   $91.3495   $91.35   $91.35   $91.30  
  Purchase #7 $203.77   12.545%   $229.3329   $229.33   $229.35   $229.30  
  7 purchase totals = $1,018.68       $1,116.4486   $1,116.46   $1,116.45   $1,116.30