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 $156.62   8.212%   $169.4816   $169.48   $169.50   $169.50  
  Purchase #2 $183.25   8.195%   $198.2673   $198.27   $198.25   $198.30  
  Purchase #3 $30.44   8.865%   $33.1385   $33.14   $33.15   $33.10  
  Purchase #4 $234.83   6.568%   $250.2536   $250.25   $250.25   $250.30  
  Purchase #5 $183.36   6.339%   $194.9832   $194.98   $195.00   $195.00  
  Purchase #6 $209.59   8.205%   $226.7869   $226.79   $226.80   $226.80  
  Purchase #7 $190.40   3.585%   $197.2258   $197.23   $197.25   $197.20  
  7 purchase totals = $1,188.49       $1,270.1369   $1,270.14   $1,270.20   $1,270.20