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 $226.26   11.750%   $252.8456   $252.85   $252.85   $252.80  
  Purchase #2 $201.84   13.788%   $229.6697   $229.67   $229.65   $229.70  
  Purchase #3 $79.54   10.588%   $87.9617   $87.96   $87.95   $88.00  
  Purchase #4 $89.82   6.840%   $95.9637   $95.96   $95.95   $96.00  
  Purchase #5 $89.83   8.680%   $97.6272   $97.63   $97.65   $97.60  
  Purchase #6 $83.39   11.545%   $93.0174   $93.02   $93.00   $93.00  
  Purchase #7 $136.75   9.346%   $149.5307   $149.53   $149.55   $149.50  
  7 purchase totals = $907.43       $1,006.6160   $1,006.62   $1,006.60   $1,006.60