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 $228.79   7.330%   $245.5603   $245.56   $245.55   $245.60  
  Purchase #2 $174.83   6.679%   $186.5069   $186.51   $186.50   $186.50  
  Purchase #3 $66.83   3.828%   $69.3883   $69.39   $69.40   $69.40  
  Purchase #4 $235.48   3.313%   $243.2815   $243.28   $243.30   $243.30  
  Purchase #5 $109.73   6.436%   $116.7922   $116.79   $116.80   $116.80  
  Purchase #6 $43.27   11.425%   $48.2136   $48.21   $48.20   $48.20  
  Purchase #7 $42.66   7.596%   $45.9005   $45.90   $45.90   $45.90  
  7 purchase totals = $901.59       $955.6433   $955.64   $955.65   $955.70