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 $241.37   13.535%   $274.0394   $274.04   $274.05   $274.00  
  Purchase #2 $142.51   6.697%   $152.0539   $152.05   $152.05   $152.10  
  Purchase #3 $80.50   5.279%   $84.7496   $84.75   $84.75   $84.70  
  Purchase #4 $242.52   9.479%   $265.5085   $265.51   $265.50   $265.50  
  Purchase #5 $157.85   5.480%   $166.5002   $166.50   $166.50   $166.50  
  Purchase #6 $116.25   3.163%   $119.927   $119.93   $119.95   $119.90  
  Purchase #7 $230.38   7.763%   $248.2644   $248.26   $248.25   $248.30  
  7 purchase totals = $1,211.38       $1,311.0430   $1,311.04   $1,311.05   $1,311.00