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 $193.63   8.483%   $210.0556   $210.06   $210.05   $210.10  
  Purchase #2 $222.32   8.554%   $241.3373   $241.34   $241.35   $241.30  
  Purchase #3 $120.33   8.362%   $130.392   $130.39   $130.40   $130.40  
  Purchase #4 $247.43   6.369%   $263.1888   $263.19   $263.20   $263.20  
  Purchase #5 $131.97   9.799%   $144.9017   $144.90   $144.90   $144.90  
  Purchase #6 $14.46   8.712%   $15.7198   $15.72   $15.70   $15.70  
  Purchase #7 $190.65   10.841%   $211.3184   $211.32   $211.30   $211.30  
  7 purchase totals = $1,120.79       $1,216.9136   $1,216.92   $1,216.90   $1,216.90