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 $219.42   13.227%   $248.4427   $248.44   $248.45   $248.40  
  Purchase #2 $58.80   11.516%   $65.5714   $65.57   $65.55   $65.60  
  Purchase #3 $223.73   5.370%   $235.7443   $235.74   $235.75   $235.70  
  Purchase #4 $150.98   9.606%   $165.4831   $165.48   $165.50   $165.50  
  Purchase #5 $236.44   12.854%   $266.832   $266.83   $266.85   $266.80  
  Purchase #6 $176.88   12.406%   $198.8237   $198.82   $198.80   $198.80  
  Purchase #7 $63.44   7.770%   $68.3693   $68.37   $68.35   $68.40  
  7 purchase totals = $1,129.69       $1,249.2665   $1,249.25   $1,249.25   $1,249.20