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 $57.90   9.678%   $63.5036   $63.50   $63.50   $63.50  
  Purchase #2 $155.88   10.230%   $171.8265   $171.83   $171.85   $171.80  
  Purchase #3 $236.95   11.419%   $264.0073   $264.01   $264.00   $264.00  
  Purchase #4 $92.64   7.655%   $99.7316   $99.73   $99.75   $99.70  
  Purchase #5 $236.77   10.816%   $262.379   $262.38   $262.40   $262.40  
  Purchase #6 $246.33   5.135%   $258.979   $258.98   $259.00   $259.00  
  Purchase #7 $131.91   3.624%   $136.6904   $136.69   $136.70   $136.70  
  7 purchase totals = $1,158.38       $1,257.1174   $1,257.12   $1,257.20   $1,257.10