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 $120.61   4.408%   $125.9265   $125.93   $125.95   $125.90  
  Purchase #2 $169.55   13.441%   $192.3392   $192.34   $192.35   $192.30  
  Purchase #3 $12.74   4.753%   $13.3455   $13.35   $13.35   $13.30  
  Purchase #4 $20.90   13.521%   $23.7259   $23.73   $23.75   $23.70  
  Purchase #5 $196.72   12.532%   $221.373   $221.37   $221.35   $221.40  
  Purchase #6 $150.88   7.373%   $162.0044   $162.00   $162.00   $162.00  
  Purchase #7 $169.86   4.152%   $176.9126   $176.91   $176.90   $176.90  
  7 purchase totals = $841.26       $915.6271   $915.63   $915.65   $915.50