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 $63.49   7.482%   $68.2403   $68.24   $68.25   $68.20  
  Purchase #2 $32.80   5.765%   $34.6909   $34.69   $34.70   $34.70  
  Purchase #3 $161.54   12.435%   $181.6275   $181.63   $181.65   $181.60  
  Purchase #4 $216.52   10.238%   $238.6873   $238.69   $238.70   $238.70  
  Purchase #5 $53.50   10.261%   $58.9896   $58.99   $59.00   $59.00  
  Purchase #6 $133.40   4.422%   $139.2989   $139.30   $139.30   $139.30  
  Purchase #7 $155.30   5.197%   $163.3709   $163.37   $163.35   $163.40  
  7 purchase totals = $816.55       $884.9054   $884.91   $884.95   $884.90