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 $128.46   5.680%   $135.7565   $135.76   $135.75   $135.80  
  Purchase #2 $214.73   8.794%   $233.6134   $233.61   $233.60   $233.60  
  Purchase #3 $178.90   13.797%   $203.5828   $203.58   $203.60   $203.60  
  Purchase #4 $19.27   6.661%   $20.5536   $20.55   $20.55   $20.60  
  Purchase #5 $186.77   13.464%   $211.9167   $211.92   $211.90   $211.90  
  Purchase #6 $24.59   3.221%   $25.382   $25.38   $25.40   $25.40  
  Purchase #7 $202.65   7.154%   $217.1476   $217.15   $217.15   $217.10  
  7 purchase totals = $955.37       $1,047.9526   $1,047.95   $1,047.95   $1,048.00