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 $56.91   7.710%   $61.2978   $61.30   $61.30   $61.30  
  Purchase #2 $170.34   10.643%   $188.4693   $188.47   $188.45   $188.50  
  Purchase #3 $232.44   6.180%   $246.8048   $246.80   $246.80   $246.80  
  Purchase #4 $150.30   8.190%   $162.6096   $162.61   $162.60   $162.60  
  Purchase #5 $10.56   13.778%   $12.015   $12.02   $12.00   $12.00  
  Purchase #6 $226.79   8.561%   $246.2055   $246.21   $246.20   $246.20  
  Purchase #7 $16.30   12.274%   $18.3007   $18.30   $18.30   $18.30  
  7 purchase totals = $863.64       $935.7027   $935.71   $935.65   $935.70