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 $201.57   7.217%   $216.1173   $216.12   $216.10   $216.10  
  Purchase #2 $47.55   11.341%   $52.9426   $52.94   $52.95   $52.90  
  Purchase #3 $56.32   5.744%   $59.555   $59.56   $59.55   $59.60  
  Purchase #4 $22.59   7.664%   $24.3213   $24.32   $24.30   $24.30  
  Purchase #5 $216.94   5.503%   $228.8782   $228.88   $228.90   $228.90  
  Purchase #6 $173.96   5.302%   $183.1834   $183.18   $183.20   $183.20  
  Purchase #7 $154.95   8.588%   $168.2571   $168.26   $168.25   $168.30  
  7 purchase totals = $873.88       $933.2549   $933.26   $933.25   $933.30