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 $198.66   12.838%   $224.164   $224.16   $224.15   $224.20  
  Purchase #2 $111.44   12.219%   $125.0569   $125.06   $125.05   $125.10  
  Purchase #3 $160.46   8.203%   $173.6225   $173.62   $173.60   $173.60  
  Purchase #4 $202.42   5.823%   $214.2069   $214.21   $214.20   $214.20  
  Purchase #5 $7.33   13.776%   $8.3398   $8.34   $8.35   $8.30  
  Purchase #6 $235.28   9.123%   $256.7446   $256.74   $256.75   $256.70  
  Purchase #7 $52.81   8.192%   $57.1362   $57.14   $57.15   $57.10  
  7 purchase totals = $968.40       $1,059.2709   $1,059.27   $1,059.25   $1,059.20