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 $232.60   13.656%   $264.3639   $264.36   $264.35   $264.40  
  Purchase #2 $41.94   5.211%   $44.1255   $44.13   $44.15   $44.10  
  Purchase #3 $245.29   10.677%   $271.4796   $271.48   $271.50   $271.50  
  Purchase #4 $204.99   13.750%   $233.1761   $233.18   $233.20   $233.20  
  Purchase #5 $228.80   3.492%   $236.7897   $236.79   $236.80   $236.80  
  Purchase #6 $205.69   10.359%   $226.9974   $227.00   $227.00   $227.00  
  Purchase #7 $76.76   12.311%   $86.2099   $86.21   $86.20   $86.20  
  7 purchase totals = $1,236.07       $1,363.1421   $1,363.15   $1,363.20   $1,363.20