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 $33.87   10.299%   $37.3583   $37.36   $37.35   $37.40  
  Purchase #2 $98.49   12.191%   $110.4969   $110.50   $110.50   $110.50  
  Purchase #3 $209.74   11.374%   $233.5958   $233.60   $233.60   $233.60  
  Purchase #4 $115.36   5.205%   $121.3645   $121.36   $121.35   $121.40  
  Purchase #5 $48.32   6.780%   $51.5961   $51.60   $51.60   $51.60  
  Purchase #6 $47.39   5.303%   $49.9031   $49.90   $49.90   $49.90  
  Purchase #7 $151.82   6.124%   $161.1175   $161.12   $161.10   $161.10  
  7 purchase totals = $704.99       $765.4322   $765.44   $765.40   $765.50