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 $122.58   8.140%   $132.558   $132.56   $132.55   $132.60  
  Purchase #2 $250.32   6.246%   $265.955   $265.96   $265.95   $266.00  
  Purchase #3 $230.37   8.103%   $249.0369   $249.04   $249.05   $249.00  
  Purchase #4 $218.74   13.519%   $248.3115   $248.31   $248.30   $248.30  
  Purchase #5 $99.69   10.352%   $110.0099   $110.01   $110.00   $110.00  
  Purchase #6 $220.90   11.293%   $245.8462   $245.85   $245.85   $245.80  
  Purchase #7 $134.50   6.558%   $143.3205   $143.32   $143.30   $143.30  
  7 purchase totals = $1,277.10       $1,395.0380   $1,395.05   $1,395.00   $1,395.00