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 $142.78   3.672%   $148.0229   $148.02   $148.00   $148.00  
  Purchase #2 $156.98   12.301%   $176.2901   $176.29   $176.30   $176.30  
  Purchase #3 $213.63   10.140%   $235.2921   $235.29   $235.30   $235.30  
  Purchase #4 $201.75   7.433%   $216.7461   $216.75   $216.75   $216.70  
  Purchase #5 $66.68   7.423%   $71.6297   $71.63   $71.65   $71.60  
  Purchase #6 $161.36   9.238%   $176.2664   $176.27   $176.25   $176.30  
  Purchase #7 $241.97   11.849%   $270.641   $270.64   $270.65   $270.60  
  7 purchase totals = $1,185.15       $1,294.8883   $1,294.89   $1,294.90   $1,294.80