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 $174.41   13.144%   $197.3345   $197.33   $197.35   $197.30  
  Purchase #2 $28.96   13.386%   $32.8366   $32.84   $32.85   $32.80  
  Purchase #3 $99.92   9.792%   $109.7042   $109.70   $109.70   $109.70  
  Purchase #4 $248.67   6.702%   $265.3359   $265.34   $265.35   $265.30  
  Purchase #5 $5.94   7.569%   $6.3896   $6.39   $6.40   $6.40  
  Purchase #6 $172.63   13.458%   $195.8625   $195.86   $195.85   $195.90  
  Purchase #7 $165.85   8.677%   $180.2408   $180.24   $180.25   $180.20  
  7 purchase totals = $896.38       $987.7041   $987.70   $987.75   $987.60