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 $81.87   13.829%   $93.1918   $93.19   $93.20   $93.20  
  Purchase #2 $246.48   4.704%   $258.0744   $258.07   $258.05   $258.10  
  Purchase #3 $200.33   7.408%   $215.1704   $215.17   $215.15   $215.20  
  Purchase #4 $238.52   12.539%   $268.428   $268.43   $268.45   $268.40  
  Purchase #5 $113.98   3.312%   $117.755   $117.76   $117.75   $117.80  
  Purchase #6 $229.31   6.792%   $244.8847   $244.88   $244.90   $244.90  
  Purchase #7 $194.55   6.513%   $207.221   $207.22   $207.20   $207.20  
  7 purchase totals = $1,305.04       $1,404.7253   $1,404.72   $1,404.70   $1,404.80