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 $34.62   6.640%   $36.9188   $36.92   $36.90   $36.90  
  Purchase #2 $123.61   8.411%   $134.0068   $134.01   $134.00   $134.00  
  Purchase #3 $176.43   4.400%   $184.1929   $184.19   $184.20   $184.20  
  Purchase #4 $152.88   6.596%   $162.964   $162.96   $162.95   $163.00  
  Purchase #5 $61.80   7.803%   $66.6223   $66.62   $66.60   $66.60  
  Purchase #6 $221.66   12.754%   $249.9305   $249.93   $249.95   $249.90  
  Purchase #7 $168.35   9.820%   $184.882   $184.88   $184.90   $184.90  
  7 purchase totals = $939.35       $1,019.5173   $1,019.51   $1,019.50   $1,019.50