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 $233.57   13.755%   $265.6976   $265.70   $265.70   $265.70  
  Purchase #2 $111.44   6.548%   $118.7371   $118.74   $118.75   $118.70  
  Purchase #3 $117.98   7.557%   $126.8957   $126.90   $126.90   $126.90  
  Purchase #4 $57.95   12.514%   $65.2019   $65.20   $65.20   $65.20  
  Purchase #5 $206.94   4.711%   $216.6889   $216.69   $216.70   $216.70  
  Purchase #6 $241.83   10.102%   $266.2597   $266.26   $266.25   $266.30  
  Purchase #7 $88.84   6.103%   $94.2619   $94.26   $94.25   $94.30  
  7 purchase totals = $1,058.55       $1,153.7428   $1,153.75   $1,153.75   $1,153.80