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 $244.46   8.831%   $266.0483   $266.05   $266.05   $266.00  
  Purchase #2 $98.32   5.161%   $103.3943   $103.39   $103.40   $103.40  
  Purchase #3 $185.96   6.543%   $198.1274   $198.13   $198.15   $198.10  
  Purchase #4 $13.66   4.349%   $14.2541   $14.25   $14.25   $14.30  
  Purchase #5 $117.40   11.568%   $130.9808   $130.98   $131.00   $131.00  
  Purchase #6 $219.32   7.129%   $234.9553   $234.96   $234.95   $235.00  
  Purchase #7 $132.83   3.237%   $137.1297   $137.13   $137.15   $137.10  
  7 purchase totals = $1,011.95       $1,084.8899   $1,084.89   $1,084.95   $1,084.90