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 $62.82   8.232%   $67.9913   $67.99   $68.00   $68.00  
  Purchase #2 $34.73   12.382%   $39.0303   $39.03   $39.05   $39.00  
  Purchase #3 $41.95   13.596%   $47.6535   $47.65   $47.65   $47.70  
  Purchase #4 $149.35   6.271%   $158.7157   $158.72   $158.70   $158.70  
  Purchase #5 $182.32   9.813%   $200.2111   $200.21   $200.20   $200.20  
  Purchase #6 $219.75   5.252%   $231.2913   $231.29   $231.30   $231.30  
  Purchase #7 $48.92   7.483%   $52.5807   $52.58   $52.60   $52.60  
  7 purchase totals = $739.84       $797.4739   $797.47   $797.50   $797.50