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 $60.66   8.296%   $65.6924   $65.69   $65.70   $65.70  
  Purchase #2 $110.26   8.499%   $119.631   $119.63   $119.65   $119.60  
  Purchase #3 $82.97   7.703%   $89.3612   $89.36   $89.35   $89.40  
  Purchase #4 $77.92   11.676%   $87.0179   $87.02   $87.00   $87.00  
  Purchase #5 $226.87   4.741%   $237.6259   $237.63   $237.65   $237.60  
  Purchase #6 $202.45   9.291%   $221.2596   $221.26   $221.25   $221.30  
  Purchase #7 $113.37   6.615%   $120.8694   $120.87   $120.85   $120.90  
  7 purchase totals = $874.50       $941.4574   $941.46   $941.45   $941.50