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 $66.26   3.567%   $68.6235   $68.62   $68.60   $68.60  
  Purchase #2 $235.65   10.542%   $260.4922   $260.49   $260.50   $260.50  
  Purchase #3 $178.32   13.722%   $202.7891   $202.79   $202.80   $202.80  
  Purchase #4 $187.25   4.337%   $195.371   $195.37   $195.35   $195.40  
  Purchase #5 $173.97   5.144%   $182.919   $182.92   $182.90   $182.90  
  Purchase #6 $200.58   5.703%   $212.0191   $212.02   $212.00   $212.00  
  Purchase #7 $127.51   6.433%   $135.7127   $135.71   $135.70   $135.70  
  7 purchase totals = $1,169.54       $1,257.9266   $1,257.92   $1,257.85   $1,257.90