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 $34.49   6.506%   $36.7339   $36.73   $36.75   $36.70  
  Purchase #2 $241.67   6.346%   $257.0064   $257.01   $257.00   $257.00  
  Purchase #3 $166.48   5.481%   $175.6048   $175.60   $175.60   $175.60  
  Purchase #4 $65.86   13.209%   $74.5594   $74.56   $74.55   $74.60  
  Purchase #5 $40.64   6.543%   $43.2991   $43.30   $43.30   $43.30  
  Purchase #6 $158.45   9.338%   $173.2461   $173.25   $173.25   $173.20  
  Purchase #7 $79.38   8.461%   $86.0963   $86.10   $86.10   $86.10  
  7 purchase totals = $786.97       $846.5460   $846.55   $846.55   $846.50