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 $57.84   5.433%   $60.9824   $60.98   $61.00   $61.00  
  Purchase #2 $138.95   3.763%   $144.1787   $144.18   $144.20   $144.20  
  Purchase #3 $190.42   3.598%   $197.2713   $197.27   $197.25   $197.30  
  Purchase #4 $80.27   7.315%   $86.1418   $86.14   $86.15   $86.10  
  Purchase #5 $242.43   3.406%   $250.6872   $250.69   $250.70   $250.70  
  Purchase #6 $133.94   3.465%   $138.581   $138.58   $138.60   $138.60  
  Purchase #7 $113.78   3.663%   $117.9478   $117.95   $117.95   $117.90  
  7 purchase totals = $957.63       $995.7902   $995.79   $995.85   $995.80