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 $183.54   13.807%   $208.8814   $208.88   $208.90   $208.90  
  Purchase #2 $192.53   6.802%   $205.6259   $205.63   $205.65   $205.60  
  Purchase #3 $39.29   9.348%   $42.9628   $42.96   $42.95   $43.00  
  Purchase #4 $54.54   11.426%   $60.7717   $60.77   $60.75   $60.80  
  Purchase #5 $149.57   4.607%   $156.4607   $156.46   $156.45   $156.50  
  Purchase #6 $12.26   4.497%   $12.8113   $12.81   $12.80   $12.80  
  Purchase #7 $69.39   5.442%   $73.1662   $73.17   $73.15   $73.20  
  7 purchase totals = $701.12       $760.6800   $760.68   $760.65   $760.80