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 $184.72   4.667%   $193.3409   $193.34   $193.35   $193.30  
  Purchase #2 $42.73   8.614%   $46.4108   $46.41   $46.40   $46.40  
  Purchase #3 $224.28   5.608%   $236.8576   $236.86   $236.85   $236.90  
  Purchase #4 $151.55   10.547%   $167.534   $167.53   $167.55   $167.50  
  Purchase #5 $162.44   11.274%   $180.7535   $180.75   $180.75   $180.80  
  Purchase #6 $228.78   11.451%   $254.9776   $254.98   $255.00   $255.00  
  Purchase #7 $215.35   9.867%   $236.5986   $236.60   $236.60   $236.60  
  7 purchase totals = $1,209.85       $1,316.4730   $1,316.47   $1,316.50   $1,316.50