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 $85.39   8.424%   $92.5833   $92.58   $92.60   $92.60  
  Purchase #2 $244.71   11.869%   $273.7546   $273.75   $273.75   $273.80  
  Purchase #3 $62.76   9.292%   $68.5917   $68.59   $68.60   $68.60  
  Purchase #4 $136.70   4.258%   $142.5207   $142.52   $142.50   $142.50  
  Purchase #5 $186.59   12.465%   $209.8484   $209.85   $209.85   $209.80  
  Purchase #6 $30.26   7.617%   $32.5649   $32.56   $32.55   $32.60  
  Purchase #7 $90.74   3.354%   $93.7834   $93.78   $93.80   $93.80  
  7 purchase totals = $837.15       $913.6470   $913.63   $913.65   $913.70