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 $84.77   9.596%   $92.9045   $92.90   $92.90   $92.90  
  Purchase #2 $205.26   3.150%   $211.7257   $211.73   $211.75   $211.70  
  Purchase #3 $104.53   11.853%   $116.9199   $116.92   $116.90   $116.90  
  Purchase #4 $242.81   4.551%   $253.8603   $253.86   $253.85   $253.90  
  Purchase #5 $206.78   6.639%   $220.5081   $220.51   $220.50   $220.50  
  Purchase #6 $12.44   9.847%   $13.665   $13.67   $13.65   $13.70  
  Purchase #7 $242.48   11.133%   $269.4753   $269.48   $269.50   $269.50  
  7 purchase totals = $1,099.07       $1,179.0588   $1,179.07   $1,179.05   $1,179.10