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 $67.53   11.756%   $75.4688   $75.47   $75.45   $75.50  
  Purchase #2 $144.96   9.156%   $158.2325   $158.23   $158.25   $158.20  
  Purchase #3 $224.26   4.305%   $233.9144   $233.91   $233.90   $233.90  
  Purchase #4 $64.45   12.227%   $72.3303   $72.33   $72.35   $72.30  
  Purchase #5 $186.98   8.633%   $203.122   $203.12   $203.10   $203.10  
  Purchase #6 $205.39   12.595%   $231.2589   $231.26   $231.25   $231.30  
  Purchase #7 $191.71   7.409%   $205.9138   $205.91   $205.90   $205.90  
  7 purchase totals = $1,085.28       $1,180.2407   $1,180.23   $1,180.20   $1,180.20