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 $195.37   3.214%   $201.6492   $201.65   $201.65   $201.60  
  Purchase #2 $182.34   3.509%   $188.7383   $188.74   $188.75   $188.70  
  Purchase #3 $16.85   7.406%   $18.0979   $18.10   $18.10   $18.10  
  Purchase #4 $61.45   5.683%   $64.9422   $64.94   $64.95   $64.90  
  Purchase #5 $35.68   5.794%   $37.7473   $37.75   $37.75   $37.70  
  Purchase #6 $135.41   7.852%   $146.0424   $146.04   $146.05   $146.00  
  Purchase #7 $186.82   5.672%   $197.4164   $197.42   $197.40   $197.40  
  7 purchase totals = $813.92       $854.6337   $854.64   $854.65   $854.40