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 $83.25   11.640%   $92.9403   $92.94   $92.95   $92.90  
  Purchase #2 $20.99   12.228%   $23.5567   $23.56   $23.55   $23.60  
  Purchase #3 $86.68   8.609%   $94.1423   $94.14   $94.15   $94.10  
  Purchase #4 $198.34   13.108%   $224.3384   $224.34   $224.35   $224.30  
  Purchase #5 $225.60   5.241%   $237.4237   $237.42   $237.40   $237.40  
  Purchase #6 $124.64   5.671%   $131.7083   $131.71   $131.70   $131.70  
  Purchase #7 $42.78   12.104%   $47.9581   $47.96   $47.95   $48.00  
  7 purchase totals = $782.28       $852.0678   $852.07   $852.05   $852.00