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 $248.26   8.330%   $268.9401   $268.94   $268.95   $268.90  
  Purchase #2 $152.52   8.703%   $165.7938   $165.79   $165.80   $165.80  
  Purchase #3 $148.45   5.643%   $156.827   $156.83   $156.85   $156.80  
  Purchase #4 $153.54   10.710%   $169.9841   $169.98   $170.00   $170.00  
  Purchase #5 $174.91   9.199%   $191   $191.00   $191.00   $191.00  
  Purchase #6 $26.75   12.397%   $30.0662   $30.07   $30.05   $30.10  
  Purchase #7 $47.51   7.387%   $51.0196   $51.02   $51.00   $51.00  
  7 purchase totals = $951.94       $1,033.6308   $1,033.63   $1,033.65   $1,033.60