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 $60.92   13.816%   $69.3367   $69.34   $69.35   $69.30  
  Purchase #2 $130.61   9.478%   $142.9892   $142.99   $143.00   $143.00  
  Purchase #3 $228.43   8.571%   $248.0087   $248.01   $248.00   $248.00  
  Purchase #4 $224.61   3.758%   $233.0508   $233.05   $233.05   $233.10  
  Purchase #5 $189.62   7.674%   $204.1714   $204.17   $204.15   $204.20  
  Purchase #6 $243.77   13.454%   $276.5668   $276.57   $276.55   $276.60  
  Purchase #7 $23.90   7.678%   $25.735   $25.74   $25.75   $25.70  
  7 purchase totals = $1,101.86       $1,199.8586   $1,199.87   $1,199.85   $1,199.90