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 $7.42   3.445%   $7.6756   $7.68   $7.70   $7.70  
  Purchase #2 $220.77   13.860%   $251.3687   $251.37   $251.35   $251.40  
  Purchase #3 $35.70   9.604%   $39.1286   $39.13   $39.15   $39.10  
  Purchase #4 $47.50   11.699%   $53.057   $53.06   $53.05   $53.10  
  Purchase #5 $76.63   4.236%   $79.876   $79.88   $79.90   $79.90  
  Purchase #6 $58.68   6.421%   $62.4478   $62.45   $62.45   $62.40  
  Purchase #7 $26.61   12.452%   $29.9235   $29.92   $29.90   $29.90  
  7 purchase totals = $473.31       $523.4772   $523.49   $523.50   $523.50