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 $197.71   6.778%   $211.1108   $211.11   $211.10   $211.10  
  Purchase #2 $217.61   12.861%   $245.5968   $245.60   $245.60   $245.60  
  Purchase #3 $180.50   11.322%   $200.9362   $200.94   $200.95   $200.90  
  Purchase #4 $220.41   9.465%   $241.2718   $241.27   $241.25   $241.30  
  Purchase #5 $115.69   11.557%   $129.0603   $129.06   $129.05   $129.10  
  Purchase #6 $91.80   6.246%   $97.5338   $97.53   $97.55   $97.50  
  Purchase #7 $68.32   13.415%   $77.4851   $77.49   $77.50   $77.50  
  7 purchase totals = $1,092.04       $1,202.9948   $1,203.00   $1,203.00   $1,203.00