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 $231.49   12.383%   $260.1554   $260.16   $260.15   $260.20  
  Purchase #2 $206.82   6.252%   $219.7504   $219.75   $219.75   $219.80  
  Purchase #3 $80.60   4.703%   $84.3906   $84.39   $84.40   $84.40  
  Purchase #4 $60.89   7.761%   $65.6157   $65.62   $65.60   $65.60  
  Purchase #5 $225.91   7.848%   $243.6394   $243.64   $243.65   $243.60  
  Purchase #6 $161.93   4.507%   $169.2282   $169.23   $169.25   $169.20  
  Purchase #7 $58.35   12.392%   $65.5807   $65.58   $65.60   $65.60  
  7 purchase totals = $1,025.99       $1,108.3604   $1,108.37   $1,108.40   $1,108.40