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 $133.40   13.761%   $151.7572   $151.76   $151.75   $151.80  
  Purchase #2 $215.66   11.327%   $240.0878   $240.09   $240.10   $240.10  
  Purchase #3 $194.86   5.273%   $205.135   $205.14   $205.15   $205.10  
  Purchase #4 $41.56   6.354%   $44.2007   $44.20   $44.20   $44.20  
  Purchase #5 $109.26   13.689%   $124.2166   $124.22   $124.20   $124.20  
  Purchase #6 $239.92   10.250%   $264.5118   $264.51   $264.50   $264.50  
  Purchase #7 $32.45   3.862%   $33.7032   $33.70   $33.70   $33.70  
  7 purchase totals = $967.11       $1,063.6123   $1,063.62   $1,063.60   $1,063.60