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 $58.65   8.544%   $63.6611   $63.66   $63.65   $63.70  
  Purchase #2 $58.59   7.168%   $62.7897   $62.79   $62.80   $62.80  
  Purchase #3 $220.42   9.725%   $241.8558   $241.86   $241.85   $241.90  
  Purchase #4 $16.84   5.319%   $17.7357   $17.74   $17.75   $17.70  
  Purchase #5 $73.34   3.607%   $75.9854   $75.99   $76.00   $76.00  
  Purchase #6 $194.36   6.138%   $206.2898   $206.29   $206.30   $206.30  
  Purchase #7 $123.86   5.445%   $130.6042   $130.60   $130.60   $130.60  
  7 purchase totals = $746.06       $798.9217   $798.93   $798.95   $799.00