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 $58.34   7.551%   $62.7453   $62.75   $62.75   $62.70  
  Purchase #2 $69.50   5.540%   $73.3503   $73.35   $73.35   $73.40  
  Purchase #3 $54.81   10.377%   $60.4976   $60.50   $60.50   $60.50  
  Purchase #4 $210.55   4.781%   $220.6164   $220.62   $220.60   $220.60  
  Purchase #5 $171.83   8.284%   $186.0644   $186.06   $186.05   $186.10  
  Purchase #6 $202.43   11.767%   $226.2499   $226.25   $226.25   $226.20  
  Purchase #7 $12.96   5.209%   $13.6351   $13.64   $13.65   $13.60  
  7 purchase totals = $780.42       $843.1590   $843.17   $843.15   $843.10