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 $63.50   12.831%   $71.6477   $71.65   $71.65   $71.60  
  Purchase #2 $242.90   9.117%   $265.0452   $265.05   $265.05   $265.00  
  Purchase #3 $152.71   7.462%   $164.1052   $164.11   $164.10   $164.10  
  Purchase #4 $135.57   4.198%   $141.2612   $141.26   $141.25   $141.30  
  Purchase #5 $138.58   9.397%   $151.6024   $151.60   $151.60   $151.60  
  Purchase #6 $148.70   6.842%   $158.8741   $158.87   $158.85   $158.90  
  Purchase #7 $223.71   7.511%   $240.5129   $240.51   $240.50   $240.50  
  7 purchase totals = $1,105.67       $1,193.0487   $1,193.05   $1,193.00   $1,193.00