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 $112.59   8.478%   $122.1354   $122.14   $122.15   $122.10  
  Purchase #2 $17.40   5.130%   $18.2926   $18.29   $18.30   $18.30  
  Purchase #3 $203.91   7.186%   $218.563   $218.56   $218.55   $218.60  
  Purchase #4 $171.64   7.165%   $183.938   $183.94   $183.95   $183.90  
  Purchase #5 $230.69   5.572%   $243.544   $243.54   $243.55   $243.50  
  Purchase #6 $11.52   3.769%   $11.9542   $11.95   $11.95   $12.00  
  Purchase #7 $149.47   5.420%   $157.5713   $157.57   $157.55   $157.60  
  7 purchase totals = $897.22       $955.9985   $955.99   $956.00   $956.00