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 $44.93   8.823%   $48.8942   $48.89   $48.90   $48.90  
  Purchase #2 $223.29   13.443%   $253.3069   $253.31   $253.30   $253.30  
  Purchase #3 $164.28   3.481%   $169.9986   $170.00   $170.00   $170.00  
  Purchase #4 $88.98   5.791%   $94.1328   $94.13   $94.15   $94.10  
  Purchase #5 $67.43   8.345%   $73.057   $73.06   $73.05   $73.10  
  Purchase #6 $199.83   10.586%   $220.984   $220.98   $221.00   $221.00  
  Purchase #7 $106.39   6.559%   $113.3681   $113.37   $113.35   $113.40  
  7 purchase totals = $895.13       $973.7416   $973.74   $973.75   $973.80