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 $187.60   9.429%   $205.2888   $205.29   $205.30   $205.30  
  Purchase #2 $210.93   10.301%   $232.6579   $232.66   $232.65   $232.70  
  Purchase #3 $230.56   10.678%   $255.1792   $255.18   $255.20   $255.20  
  Purchase #4 $123.79   8.602%   $134.4384   $134.44   $134.45   $134.40  
  Purchase #5 $95.66   8.323%   $103.6218   $103.62   $103.60   $103.60  
  Purchase #6 $209.74   3.828%   $217.7688   $217.77   $217.75   $217.80  
  Purchase #7 $237.51   4.495%   $248.1861   $248.19   $248.20   $248.20  
  7 purchase totals = $1,295.79       $1,397.1410   $1,397.15   $1,397.15   $1,397.20