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 $69.84   8.388%   $75.6982   $75.70   $75.70   $75.70  
  Purchase #2 $68.71   10.147%   $75.682   $75.68   $75.70   $75.70  
  Purchase #3 $150.83   6.656%   $160.8692   $160.87   $160.85   $160.90  
  Purchase #4 $92.76   3.364%   $95.8804   $95.88   $95.90   $95.90  
  Purchase #5 $135.37   8.716%   $147.1688   $147.17   $147.15   $147.20  
  Purchase #6 $223.34   13.680%   $253.8929   $253.89   $253.90   $253.90  
  Purchase #7 $234.28   5.312%   $246.725   $246.73   $246.75   $246.70  
  7 purchase totals = $975.13       $1,055.9165   $1,055.92   $1,055.95   $1,056.00