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 $208.88   3.756%   $216.7255   $216.73   $216.75   $216.70  
  Purchase #2 $147.93   13.319%   $167.6328   $167.63   $167.65   $167.60  
  Purchase #3 $125.93   11.628%   $140.5731   $140.57   $140.55   $140.60  
  Purchase #4 $212.33   12.528%   $238.9307   $238.93   $238.95   $238.90  
  Purchase #5 $144.36   8.866%   $157.159   $157.16   $157.15   $157.20  
  Purchase #6 $62.30   8.427%   $67.55   $67.55   $67.55   $67.60  
  Purchase #7 $57.52   4.755%   $60.2551   $60.26   $60.25   $60.30  
  7 purchase totals = $959.25       $1,048.8262   $1,048.83   $1,048.85   $1,048.90