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 $238.94   5.713%   $252.5906   $252.59   $252.60   $252.60  
  Purchase #2 $176.89   11.726%   $197.6321   $197.63   $197.65   $197.60  
  Purchase #3 $19.78   13.598%   $22.4697   $22.47   $22.45   $22.50  
  Purchase #4 $124.76   7.413%   $134.0085   $134.01   $134.00   $134.00  
  Purchase #5 $52.83   3.425%   $54.6394   $54.64   $54.65   $54.60  
  Purchase #6 $60.99   6.623%   $65.0294   $65.03   $65.05   $65.00  
  Purchase #7 $102.52   8.394%   $111.1255   $111.13   $111.15   $111.10  
  7 purchase totals = $776.71       $837.4952   $837.50   $837.55   $837.40