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 $61.32   7.418%   $65.8687   $65.87   $65.85   $65.90  
  Purchase #2 $248.59   8.307%   $269.2404   $269.24   $269.25   $269.20  
  Purchase #3 $126.86   8.288%   $137.3742   $137.37   $137.35   $137.40  
  Purchase #4 $157.60   13.133%   $178.2976   $178.30   $178.30   $178.30  
  Purchase #5 $175.55   13.742%   $199.6741   $199.67   $199.65   $199.70  
  Purchase #6 $217.67   7.145%   $233.2225   $233.22   $233.20   $233.20  
  Purchase #7 $109.88   12.490%   $123.604   $123.60   $123.60   $123.60  
  7 purchase totals = $1,097.47       $1,207.2815   $1,207.27   $1,207.20   $1,207.30