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 $32.45   6.788%   $34.6527   $34.65   $34.65   $34.70  
  Purchase #2 $183.97   8.156%   $198.9746   $198.97   $198.95   $199.00  
  Purchase #3 $88.89   5.437%   $93.7229   $93.72   $93.70   $93.70  
  Purchase #4 $112.66   10.239%   $124.1953   $124.20   $124.20   $124.20  
  Purchase #5 $65.53   5.350%   $69.0359   $69.04   $69.05   $69.00  
  Purchase #6 $209.93   9.870%   $230.6501   $230.65   $230.65   $230.70  
  Purchase #7 $43.83   7.533%   $47.1317   $47.13   $47.15   $47.10  
  7 purchase totals = $737.26       $798.3632   $798.36   $798.35   $798.40