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 $189.35   9.776%   $207.8609   $207.86   $207.85   $207.90  
  Purchase #2 $91.83   6.356%   $97.6667   $97.67   $97.65   $97.70  
  Purchase #3 $40.67   8.176%   $43.9952   $44.00   $44.00   $44.00  
  Purchase #4 $79.99   9.596%   $87.6658   $87.67   $87.65   $87.70  
  Purchase #5 $99.58   7.196%   $106.7458   $106.75   $106.75   $106.70  
  Purchase #6 $162.26   12.785%   $183.0049   $183.00   $183.00   $183.00  
  Purchase #7 $18.90   11.591%   $21.0907   $21.09   $21.10   $21.10  
  7 purchase totals = $682.58       $748.0300   $748.04   $748.00   $748.10