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 $95.47   5.328%   $100.5566   $100.56   $100.55   $100.60  
  Purchase #2 $218.75   6.222%   $232.3606   $232.36   $232.35   $232.40  
  Purchase #3 $87.89   4.847%   $92.15   $92.15   $92.15   $92.20  
  Purchase #4 $238.59   12.457%   $268.3112   $268.31   $268.30   $268.30  
  Purchase #5 $215.76   12.374%   $242.4581   $242.46   $242.45   $242.50  
  Purchase #6 $127.63   8.210%   $138.1084   $138.11   $138.10   $138.10  
  Purchase #7 $144.82   10.515%   $160.0478   $160.05   $160.05   $160.00  
  7 purchase totals = $1,128.91       $1,233.9927   $1,234.00   $1,233.95   $1,234.10