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 $194.35   6.752%   $207.4725   $207.47   $207.45   $207.50  
  Purchase #2 $26.67   9.573%   $29.2231   $29.22   $29.20   $29.20  
  Purchase #3 $79.77   7.439%   $85.7041   $85.70   $85.70   $85.70  
  Purchase #4 $184.45   11.795%   $206.2059   $206.21   $206.20   $206.20  
  Purchase #5 $63.89   12.592%   $71.935   $71.94   $71.95   $71.90  
  Purchase #6 $63.84   6.532%   $68.01   $68.01   $68.00   $68.00  
  Purchase #7 $245.54   13.761%   $279.3288   $279.33   $279.35   $279.30  
  7 purchase totals = $858.51       $947.8794   $947.88   $947.85   $947.80