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 $178.30   10.354%   $196.7612   $196.76   $196.75   $196.80  
  Purchase #2 $84.47   5.168%   $88.8354   $88.84   $88.85   $88.80  
  Purchase #3 $146.51   11.217%   $162.944   $162.94   $162.95   $162.90  
  Purchase #4 $200.95   11.462%   $223.9829   $223.98   $224.00   $224.00  
  Purchase #5 $244.98   10.756%   $271.33   $271.33   $271.35   $271.30  
  Purchase #6 $119.79   11.170%   $133.1705   $133.17   $133.15   $133.20  
  Purchase #7 $197.29   11.370%   $219.7219   $219.72   $219.70   $219.70  
  7 purchase totals = $1,172.29       $1,296.7459   $1,296.74   $1,296.75   $1,296.70