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 $186.33   4.755%   $195.19   $195.19   $195.20   $195.20  
  Purchase #2 $240.81   4.651%   $252.0101   $252.01   $252.00   $252.00  
  Purchase #3 $98.89   13.124%   $111.8683   $111.87   $111.85   $111.90  
  Purchase #4 $112.63   8.772%   $122.5099   $122.51   $122.50   $122.50  
  Purchase #5 $51.37   12.322%   $57.6998   $57.70   $57.70   $57.70  
  Purchase #6 $119.94   11.168%   $133.3349   $133.33   $133.35   $133.30  
  Purchase #7 $148.86   5.783%   $157.4686   $157.47   $157.45   $157.50  
  7 purchase totals = $958.83       $1,030.0816   $1,030.08   $1,030.05   $1,030.10