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 $152.62   8.291%   $165.2737   $165.27   $165.25   $165.30  
  Purchase #2 $151.25   10.830%   $167.6304   $167.63   $167.65   $167.60  
  Purchase #3 $156.86   8.259%   $169.8151   $169.82   $169.80   $169.80  
  Purchase #4 $113.63   9.840%   $124.8112   $124.81   $124.80   $124.80  
  Purchase #5 $120.42   11.685%   $134.4911   $134.49   $134.50   $134.50  
  Purchase #6 $66.62   8.785%   $72.4726   $72.47   $72.45   $72.50  
  Purchase #7 $202.54   5.335%   $213.3455   $213.35   $213.35   $213.30  
  7 purchase totals = $963.94       $1,047.8396   $1,047.84   $1,047.80   $1,047.80