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 $111.70   9.197%   $121.973   $121.97   $121.95   $122.00  
  Purchase #2 $217.75   13.387%   $246.9002   $246.90   $246.90   $246.90  
  Purchase #3 $95.70   13.308%   $108.4358   $108.44   $108.45   $108.40  
  Purchase #4 $67.46   11.746%   $75.3839   $75.38   $75.40   $75.40  
  Purchase #5 $183.94   10.572%   $203.3861   $203.39   $203.40   $203.40  
  Purchase #6 $187.53   7.161%   $200.959   $200.96   $200.95   $201.00  
  Purchase #7 $35.65   4.257%   $37.1676   $37.17   $37.15   $37.20  
  7 purchase totals = $899.73       $994.2056   $994.21   $994.20   $994.30