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 $230.73   10.176%   $254.2091   $254.21   $254.20   $254.20  
  Purchase #2 $6.45   13.857%   $7.3438   $7.34   $7.35   $7.30  
  Purchase #3 $62.61   4.398%   $65.3636   $65.36   $65.35   $65.40  
  Purchase #4 $226.72   3.655%   $235.0066   $235.01   $235.00   $235.00  
  Purchase #5 $97.72   6.686%   $104.2536   $104.25   $104.25   $104.30  
  Purchase #6 $240.66   11.208%   $267.6332   $267.63   $267.65   $267.60  
  Purchase #7 $78.78   13.417%   $89.3499   $89.35   $89.35   $89.30  
  7 purchase totals = $943.67       $1,023.1598   $1,023.15   $1,023.15   $1,023.10