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 $84.62   5.458%   $89.2386   $89.24   $89.25   $89.20  
  Purchase #2 $197.36   3.197%   $203.6696   $203.67   $203.65   $203.70  
  Purchase #3 $70.75   3.549%   $73.2609   $73.26   $73.25   $73.30  
  Purchase #4 $221.93   10.489%   $245.2082   $245.21   $245.20   $245.20  
  Purchase #5 $169.97   4.511%   $177.6373   $177.64   $177.65   $177.60  
  Purchase #6 $205.42   13.763%   $233.692   $233.69   $233.70   $233.70  
  Purchase #7 $233.35   7.231%   $250.2235   $250.22   $250.20   $250.20  
  7 purchase totals = $1,183.40       $1,272.9301   $1,272.93   $1,272.90   $1,272.90