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 $193.57   10.729%   $214.3381   $214.34   $214.35   $214.30  
  Purchase #2 $94.95   6.638%   $101.2528   $101.25   $101.25   $101.30  
  Purchase #3 $77.95   5.257%   $82.0478   $82.05   $82.05   $82.00  
  Purchase #4 $225.65   12.589%   $254.0571   $254.06   $254.05   $254.10  
  Purchase #5 $54.56   13.191%   $61.757   $61.76   $61.75   $61.80  
  Purchase #6 $45.75   13.603%   $51.9734   $51.97   $51.95   $52.00  
  Purchase #7 $60.86   12.344%   $68.3726   $68.37   $68.35   $68.40  
  7 purchase totals = $753.29       $833.7988   $833.80   $833.75   $833.90