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 $55.48   12.732%   $62.5437   $62.54   $62.55   $62.50  
  Purchase #2 $249.49   12.838%   $281.5195   $281.52   $281.50   $281.50  
  Purchase #3 $168.53   12.575%   $189.7226   $189.72   $189.70   $189.70  
  Purchase #4 $139.33   5.277%   $146.6824   $146.68   $146.70   $146.70  
  Purchase #5 $239.73   5.511%   $252.9415   $252.94   $252.95   $252.90  
  Purchase #6 $15.47   6.186%   $16.427   $16.43   $16.45   $16.40  
  Purchase #7 $10.84   8.425%   $11.7533   $11.75   $11.75   $11.80  
  7 purchase totals = $878.87       $961.5900   $961.58   $961.60   $961.50