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 $86.46   11.311%   $96.2395   $96.24   $96.25   $96.20  
  Purchase #2 $44.86   13.660%   $50.9879   $50.99   $51.00   $51.00  
  Purchase #3 $121.83   11.269%   $135.559   $135.56   $135.55   $135.60  
  Purchase #4 $195.55   10.564%   $216.2079   $216.21   $216.20   $216.20  
  Purchase #5 $211.52   11.759%   $236.3926   $236.39   $236.40   $236.40  
  Purchase #6 $234.50   8.689%   $254.8757   $254.88   $254.90   $254.90  
  Purchase #7 $83.42   8.676%   $90.6575   $90.66   $90.65   $90.70  
  7 purchase totals = $978.14       $1,080.9201   $1,080.93   $1,080.95   $1,081.00