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 $11.25   9.750%   $12.3469   $12.35   $12.35   $12.30  
  Purchase #2 $106.89   9.434%   $116.974   $116.97   $116.95   $117.00  
  Purchase #3 $107.91   12.457%   $121.3523   $121.35   $121.35   $121.40  
  Purchase #4 $101.83   9.132%   $111.1291   $111.13   $111.15   $111.10  
  Purchase #5 $170.69   5.218%   $179.5966   $179.60   $179.60   $179.60  
  Purchase #6 $67.82   9.842%   $74.4948   $74.49   $74.50   $74.50  
  Purchase #7 $20.47   9.766%   $22.4691   $22.47   $22.45   $22.50  
  7 purchase totals = $586.86       $638.3628   $638.36   $638.35   $638.40