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 $209.27   9.792%   $229.7617   $229.76   $229.75   $229.80  
  Purchase #2 $113.49   5.488%   $119.7183   $119.72   $119.70   $119.70  
  Purchase #3 $23.89   4.791%   $25.0346   $25.03   $25.05   $25.00  
  Purchase #4 $112.73   8.614%   $122.4406   $122.44   $122.45   $122.40  
  Purchase #5 $134.52   12.729%   $151.6431   $151.64   $151.65   $151.60  
  Purchase #6 $230.89   9.811%   $253.5426   $253.54   $253.55   $253.50  
  Purchase #7 $155.62   13.620%   $176.8154   $176.82   $176.80   $176.80  
  7 purchase totals = $980.41       $1,078.9563   $1,078.95   $1,078.95   $1,078.80