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 $205.27   10.438%   $226.6961   $226.70   $226.70   $226.70  
  Purchase #2 $102.41   4.841%   $107.3677   $107.37   $107.35   $107.40  
  Purchase #3 $212.26   13.183%   $240.2422   $240.24   $240.25   $240.20  
  Purchase #4 $150.93   8.599%   $163.9085   $163.91   $163.90   $163.90  
  Purchase #5 $161.93   6.235%   $172.0263   $172.03   $172.05   $172.00  
  Purchase #6 $23.58   4.426%   $24.6237   $24.62   $24.60   $24.60  
  Purchase #7 $15.58   4.549%   $16.2887   $16.29   $16.30   $16.30  
  7 purchase totals = $871.96       $951.1532   $951.16   $951.15   $951.10