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 $203.41   9.654%   $223.0472   $223.05   $223.05   $223.00  
  Purchase #2 $186.92   8.395%   $202.6119   $202.61   $202.60   $202.60  
  Purchase #3 $87.63   4.836%   $91.8678   $91.87   $91.85   $91.90  
  Purchase #4 $248.60   5.859%   $263.1655   $263.17   $263.15   $263.20  
  Purchase #5 $5.75   6.291%   $6.1117   $6.11   $6.10   $6.10  
  Purchase #6 $195.46   4.391%   $204.0426   $204.04   $204.05   $204.00  
  Purchase #7 $245.45   8.224%   $265.6358   $265.64   $265.65   $265.60  
  7 purchase totals = $1,173.22       $1,256.4825   $1,256.49   $1,256.45   $1,256.40