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 $88.31   9.162%   $96.401   $96.40   $96.40   $96.40  
  Purchase #2 $10.83   8.302%   $11.7291   $11.73   $11.75   $11.70  
  Purchase #3 $42.92   11.629%   $47.9112   $47.91   $47.90   $47.90  
  Purchase #4 $227.75   5.506%   $240.2899   $240.29   $240.30   $240.30  
  Purchase #5 $63.44   10.181%   $69.8988   $69.90   $69.90   $69.90  
  Purchase #6 $73.94   9.645%   $81.0715   $81.07   $81.05   $81.10  
  Purchase #7 $50.86   8.261%   $55.0615   $55.06   $55.05   $55.10  
  7 purchase totals = $558.05       $602.3630   $602.36   $602.35   $602.40