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 $54.63   13.458%   $61.9821   $61.98   $62.00   $62.00  
  Purchase #2 $171.34   12.595%   $192.9203   $192.92   $192.90   $192.90  
  Purchase #3 $140.33   11.378%   $156.2967   $156.30   $156.30   $156.30  
  Purchase #4 $48.81   7.203%   $52.3258   $52.33   $52.35   $52.30  
  Purchase #5 $113.77   12.363%   $127.8354   $127.84   $127.85   $127.80  
  Purchase #6 $94.92   12.752%   $107.0242   $107.02   $107.00   $107.00  
  Purchase #7 $14.62   4.503%   $15.2783   $15.28   $15.30   $15.30  
  7 purchase totals = $638.42       $713.6628   $713.67   $713.70   $713.60