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 $58.91   6.772%   $62.8994   $62.90   $62.90   $62.90  
  Purchase #2 $247.93   3.626%   $256.9199   $256.92   $256.90   $256.90  
  Purchase #3 $189.49   12.396%   $212.9792   $212.98   $213.00   $213.00  
  Purchase #4 $194.32   3.252%   $200.6393   $200.64   $200.65   $200.60  
  Purchase #5 $100.74   5.725%   $106.5074   $106.51   $106.50   $106.50  
  Purchase #6 $126.63   13.125%   $143.2502   $143.25   $143.25   $143.30  
  Purchase #7 $32.81   8.300%   $35.5332   $35.53   $35.55   $35.50  
  7 purchase totals = $950.83       $1,018.7286   $1,018.73   $1,018.75   $1,018.70