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 $23.69   7.416%   $25.4469   $25.45   $25.45   $25.40  
  Purchase #2 $247.81   3.652%   $256.86   $256.86   $256.85   $256.90  
  Purchase #3 $207.83   4.808%   $217.8225   $217.82   $217.80   $217.80  
  Purchase #4 $82.64   10.428%   $91.2577   $91.26   $91.25   $91.30  
  Purchase #5 $147.52   11.157%   $163.9788   $163.98   $164.00   $164.00  
  Purchase #6 $8.33   4.579%   $8.7114   $8.71   $8.70   $8.70  
  Purchase #7 $245.94   3.448%   $254.42   $254.42   $254.40   $254.40  
  7 purchase totals = $963.76       $1,018.4973   $1,018.50   $1,018.45   $1,018.50