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 $198.65   3.144%   $204.8956   $204.90   $204.90   $204.90  
  Purchase #2 $167.54   3.831%   $173.9585   $173.96   $173.95   $174.00  
  Purchase #3 $118.44   3.874%   $123.0284   $123.03   $123.05   $123.00  
  Purchase #4 $100.43   6.169%   $106.6255   $106.63   $106.65   $106.60  
  Purchase #5 $109.66   13.629%   $124.6056   $124.61   $124.60   $124.60  
  Purchase #6 $53.98   12.833%   $60.9073   $60.91   $60.90   $60.90  
  Purchase #7 $126.67   10.498%   $139.9678   $139.97   $139.95   $140.00  
  7 purchase totals = $875.37       $933.9887   $934.01   $934.00   $934.00