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 $208.51   10.212%   $229.803   $229.80   $229.80   $229.80  
  Purchase #2 $61.47   5.142%   $64.6308   $64.63   $64.65   $64.60  
  Purchase #3 $104.99   13.732%   $119.4072   $119.41   $119.40   $119.40  
  Purchase #4 $84.78   7.474%   $91.1165   $91.12   $91.10   $91.10  
  Purchase #5 $175.66   8.526%   $190.6368   $190.64   $190.65   $190.60  
  Purchase #6 $165.81   5.324%   $174.6377   $174.64   $174.65   $174.60  
  Purchase #7 $174.66   6.392%   $185.8243   $185.82   $185.80   $185.80  
  7 purchase totals = $975.88       $1,056.0563   $1,056.06   $1,056.05   $1,055.90