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 $68.57   10.872%   $76.0249   $76.02   $76.00   $76.00  
  Purchase #2 $94.38   9.434%   $103.2838   $103.28   $103.30   $103.30  
  Purchase #3 $22.70   8.702%   $24.6754   $24.68   $24.70   $24.70  
  Purchase #4 $184.45   9.650%   $202.2494   $202.25   $202.25   $202.20  
  Purchase #5 $210.70   6.705%   $224.8274   $224.83   $224.85   $224.80  
  Purchase #6 $122.72   5.811%   $129.8513   $129.85   $129.85   $129.90  
  Purchase #7 $120.38   10.236%   $132.7021   $132.70   $132.70   $132.70  
  7 purchase totals = $823.90       $893.6143   $893.61   $893.65   $893.60