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 $82.92   12.695%   $93.4467   $93.45   $93.45   $93.40  
  Purchase #2 $209.36   10.162%   $230.6352   $230.64   $230.65   $230.60  
  Purchase #3 $223.93   4.330%   $233.6262   $233.63   $233.65   $233.60  
  Purchase #4 $51.63   4.255%   $53.8269   $53.83   $53.85   $53.80  
  Purchase #5 $162.85   3.634%   $168.768   $168.77   $168.75   $168.80  
  Purchase #6 $14.26   13.331%   $16.161   $16.16   $16.15   $16.20  
  Purchase #7 $53.66   11.199%   $59.6694   $59.67   $59.65   $59.70  
  7 purchase totals = $798.61       $856.1334   $856.15   $856.15   $856.10