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 $62.73   6.509%   $66.8131   $66.81   $66.80   $66.80  
  Purchase #2 $82.30   3.216%   $84.9468   $84.95   $84.95   $84.90  
  Purchase #3 $162.33   13.856%   $184.8224   $184.82   $184.80   $184.80  
  Purchase #4 $192.41   4.861%   $201.7631   $201.76   $201.75   $201.80  
  Purchase #5 $45.86   12.137%   $51.426   $51.43   $51.45   $51.40  
  Purchase #6 $201.73   7.257%   $216.3695   $216.37   $216.35   $216.40  
  Purchase #7 $244.33   4.766%   $255.9748   $255.97   $255.95   $256.00  
  7 purchase totals = $991.69       $1,062.1157   $1,062.11   $1,062.05   $1,062.10