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 $232.99   11.204%   $259.0942   $259.09   $259.10   $259.10  
  Purchase #2 $101.52   12.846%   $114.5613   $114.56   $114.55   $114.60  
  Purchase #3 $192.52   7.366%   $206.701   $206.70   $206.70   $206.70  
  Purchase #4 $25.29   8.580%   $27.4599   $27.46   $27.45   $27.50  
  Purchase #5 $71.94   6.486%   $76.606   $76.61   $76.60   $76.60  
  Purchase #6 $54.70   7.154%   $58.6132   $58.61   $58.60   $58.60  
  Purchase #7 $35.29   7.245%   $37.8468   $37.85   $37.85   $37.80  
  7 purchase totals = $714.25       $780.8824   $780.88   $780.85   $780.90