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 $46.33   10.311%   $51.1071   $51.11   $51.10   $51.10  
  Purchase #2 $218.26   10.266%   $240.6666   $240.67   $240.65   $240.70  
  Purchase #3 $232.28   4.296%   $242.2587   $242.26   $242.25   $242.30  
  Purchase #4 $111.59   6.637%   $118.9962   $119.00   $119.00   $119.00  
  Purchase #5 $11.85   6.482%   $12.6181   $12.62   $12.60   $12.60  
  Purchase #6 $169.31   4.113%   $176.2737   $176.27   $176.25   $176.30  
  Purchase #7 $164.73   12.760%   $185.7495   $185.75   $185.75   $185.70  
  7 purchase totals = $954.35       $1,027.6699   $1,027.68   $1,027.60   $1,027.70