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 $211.67   3.698%   $219.4976   $219.50   $219.50   $219.50  
  Purchase #2 $173.90   12.158%   $195.0428   $195.04   $195.05   $195.00  
  Purchase #3 $244.89   3.456%   $253.3534   $253.35   $253.35   $253.40  
  Purchase #4 $197.58   9.700%   $216.7453   $216.75   $216.75   $216.70  
  Purchase #5 $239.25   7.792%   $257.8924   $257.89   $257.90   $257.90  
  Purchase #6 $153.96   13.136%   $174.1842   $174.18   $174.20   $174.20  
  Purchase #7 $147.82   3.294%   $152.6892   $152.69   $152.70   $152.70  
  7 purchase totals = $1,369.07       $1,469.4049   $1,469.40   $1,469.45   $1,469.40