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 $98.63   11.490%   $109.9626   $109.96   $109.95   $110.00  
  Purchase #2 $114.51   6.199%   $121.6085   $121.61   $121.60   $121.60  
  Purchase #3 $191.28   10.826%   $211.988   $211.99   $212.00   $212.00  
  Purchase #4 $110.83   11.777%   $123.8824   $123.88   $123.90   $123.90  
  Purchase #5 $220.37   10.164%   $242.7684   $242.77   $242.75   $242.80  
  Purchase #6 $155.25   12.867%   $175.226   $175.23   $175.25   $175.20  
  Purchase #7 $64.58   4.140%   $67.2536   $67.25   $67.25   $67.30  
  7 purchase totals = $955.45       $1,052.6895   $1,052.69   $1,052.70   $1,052.80