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 $59.39   10.577%   $65.6717   $65.67   $65.65   $65.70  
  Purchase #2 $61.99   10.178%   $68.2993   $68.30   $68.30   $68.30  
  Purchase #3 $204.56   7.801%   $220.5177   $220.52   $220.50   $220.50  
  Purchase #4 $229.71   11.782%   $256.7744   $256.77   $256.75   $256.80  
  Purchase #5 $237.69   4.286%   $247.8774   $247.88   $247.90   $247.90  
  Purchase #6 $47.94   5.221%   $50.4429   $50.44   $50.45   $50.40  
  Purchase #7 $227.36   12.468%   $255.7072   $255.71   $255.70   $255.70  
  7 purchase totals = $1,068.64       $1,165.2906   $1,165.29   $1,165.25   $1,165.30