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 $82.30   6.372%   $87.5442   $87.54   $87.55   $87.50  
  Purchase #2 $113.57   10.779%   $125.8117   $125.81   $125.80   $125.80  
  Purchase #3 $172.75   13.591%   $196.2285   $196.23   $196.25   $196.20  
  Purchase #4 $233.68   12.313%   $262.453   $262.45   $262.45   $262.50  
  Purchase #5 $111.84   11.600%   $124.8134   $124.81   $124.80   $124.80  
  Purchase #6 $202.90   7.182%   $217.4723   $217.47   $217.45   $217.50  
  Purchase #7 $165.93   13.492%   $188.3173   $188.32   $188.30   $188.30  
  7 purchase totals = $1,082.97       $1,202.6404   $1,202.63   $1,202.60   $1,202.60