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 $61.71   10.242%   $68.0303   $68.03   $68.05   $68.00  
  Purchase #2 $29.47   5.702%   $31.1504   $31.15   $31.15   $31.20  
  Purchase #3 $110.86   13.271%   $125.5722   $125.57   $125.55   $125.60  
  Purchase #4 $24.47   13.389%   $27.7463   $27.75   $27.75   $27.70  
  Purchase #5 $30.91   8.297%   $33.4746   $33.47   $33.45   $33.50  
  Purchase #6 $91.36   10.153%   $100.6358   $100.64   $100.65   $100.60  
  Purchase #7 $46.69   11.827%   $52.212   $52.21   $52.20   $52.20  
  7 purchase totals = $395.47       $438.8216   $438.82   $438.80   $438.80