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 $63.33   8.802%   $68.9043   $68.90   $68.90   $68.90  
  Purchase #2 $12.70   11.245%   $14.1281   $14.13   $14.15   $14.10  
  Purchase #3 $46.84   6.214%   $49.7506   $49.75   $49.75   $49.80  
  Purchase #4 $250.97   12.341%   $281.9422   $281.94   $281.95   $281.90  
  Purchase #5 $136.94   3.388%   $141.5795   $141.58   $141.60   $141.60  
  Purchase #6 $12.54   9.357%   $13.7134   $13.71   $13.70   $13.70  
  Purchase #7 $233.80   8.861%   $254.517   $254.52   $254.50   $254.50  
  7 purchase totals = $757.12       $824.5351   $824.53   $824.55   $824.50