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 $72.56   5.137%   $76.2874   $76.29   $76.30   $76.30  
  Purchase #2 $184.83   8.747%   $200.9971   $201.00   $201.00   $201.00  
  Purchase #3 $181.99   9.109%   $198.5675   $198.57   $198.55   $198.60  
  Purchase #4 $169.65   12.255%   $190.4406   $190.44   $190.45   $190.40  
  Purchase #5 $28.95   4.567%   $30.2721   $30.27   $30.25   $30.30  
  Purchase #6 $21.50   3.214%   $22.191   $22.19   $22.20   $22.20  
  Purchase #7 $235.59   9.518%   $258.0135   $258.01   $258.00   $258.00  
  7 purchase totals = $895.07       $976.7692   $976.77   $976.75   $976.80