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 $43.85   7.474%   $47.1273   $47.13   $47.15   $47.10  
  Purchase #2 $231.68   11.193%   $257.6119   $257.61   $257.60   $257.60  
  Purchase #3 $81.41   9.677%   $89.288   $89.29   $89.30   $89.30  
  Purchase #4 $70.70   6.483%   $75.2835   $75.28   $75.30   $75.30  
  Purchase #5 $112.99   3.197%   $116.6023   $116.60   $116.60   $116.60  
  Purchase #6 $39.95   11.679%   $44.6158   $44.62   $44.60   $44.60  
  Purchase #7 $228.86   11.346%   $254.8265   $254.83   $254.85   $254.80  
  7 purchase totals = $809.44       $885.3553   $885.36   $885.40   $885.30