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 $125.52   7.361%   $134.7595   $134.76   $134.75   $134.80  
  Purchase #2 $30.86   5.804%   $32.6511   $32.65   $32.65   $32.70  
  Purchase #3 $51.86   13.143%   $58.676   $58.68   $58.70   $58.70  
  Purchase #4 $127.83   5.193%   $134.4682   $134.47   $134.45   $134.50  
  Purchase #5 $194.94   13.696%   $221.639   $221.64   $221.65   $221.60  
  Purchase #6 $159.42   11.365%   $177.5381   $177.54   $177.55   $177.50  
  Purchase #7 $124.33   11.293%   $138.3706   $138.37   $138.35   $138.40  
  7 purchase totals = $814.76       $898.1025   $898.11   $898.10   $898.20