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 $220.47   5.408%   $232.393   $232.39   $232.40   $232.40  
  Purchase #2 $61.46   7.214%   $65.8937   $65.89   $65.90   $65.90  
  Purchase #3 $147.95   3.197%   $152.68   $152.68   $152.70   $152.70  
  Purchase #4 $52.67   9.423%   $57.6331   $57.63   $57.65   $57.60  
  Purchase #5 $211.26   11.250%   $235.0268   $235.03   $235.05   $235.00  
  Purchase #6 $60.60   5.639%   $64.0172   $64.02   $64.00   $64.00  
  Purchase #7 $15.25   6.465%   $16.2359   $16.24   $16.25   $16.20  
  7 purchase totals = $769.66       $823.8797   $823.88   $823.95   $823.80