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 $128.62   13.468%   $145.9425   $145.94   $145.95   $145.90  
  Purchase #2 $144.72   8.314%   $156.752   $156.75   $156.75   $156.80  
  Purchase #3 $21.92   7.212%   $23.5009   $23.50   $23.50   $23.50  
  Purchase #4 $160.27   6.236%   $170.2644   $170.26   $170.25   $170.30  
  Purchase #5 $228.44   13.654%   $259.6312   $259.63   $259.65   $259.60  
  Purchase #6 $234.63   8.665%   $254.9607   $254.96   $254.95   $255.00  
  Purchase #7 $7.71   9.427%   $8.4368   $8.44   $8.45   $8.40  
  7 purchase totals = $926.31       $1,019.4885   $1,019.48   $1,019.50   $1,019.50