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 $136.40   12.717%   $153.746   $153.75   $153.75   $153.70  
  Purchase #2 $23.39   9.250%   $25.5536   $25.55   $25.55   $25.60  
  Purchase #3 $15.96   10.811%   $17.6854   $17.69   $17.70   $17.70  
  Purchase #4 $84.27   12.871%   $95.1164   $95.12   $95.10   $95.10  
  Purchase #5 $186.95   8.615%   $203.0557   $203.06   $203.05   $203.10  
  Purchase #6 $244.54   5.506%   $258.0044   $258.00   $258.00   $258.00  
  Purchase #7 $204.69   4.615%   $214.1364   $214.14   $214.15   $214.10  
  7 purchase totals = $896.20       $967.2979   $967.31   $967.30   $967.30