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 $55.51   13.236%   $62.8573   $62.86   $62.85   $62.90  
  Purchase #2 $185.78   4.417%   $193.9859   $193.99   $194.00   $194.00  
  Purchase #3 $143.92   9.798%   $158.0213   $158.02   $158.00   $158.00  
  Purchase #4 $19.37   13.832%   $22.0493   $22.05   $22.05   $22.00  
  Purchase #5 $71.94   7.642%   $77.4377   $77.44   $77.45   $77.40  
  Purchase #6 $65.84   5.408%   $69.4006   $69.40   $69.40   $69.40  
  Purchase #7 $85.86   5.208%   $90.3316   $90.33   $90.35   $90.30  
  7 purchase totals = $628.22       $674.0837   $674.09   $674.10   $674.00