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 $178.47   13.422%   $202.4242   $202.42   $202.40   $202.40  
  Purchase #2 $88.41   7.731%   $95.245   $95.25   $95.25   $95.20  
  Purchase #3 $22.76   11.621%   $25.4049   $25.40   $25.40   $25.40  
  Purchase #4 $63.56   6.217%   $67.5115   $67.51   $67.50   $67.50  
  Purchase #5 $210.65   9.412%   $230.4764   $230.48   $230.50   $230.50  
  Purchase #6 $193.33   10.673%   $213.9641   $213.96   $213.95   $214.00  
  Purchase #7 $162.26   3.288%   $167.5951   $167.60   $167.60   $167.60  
  7 purchase totals = $919.44       $1,002.6212   $1,002.62   $1,002.60   $1,002.60