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 $192.45   6.138%   $204.2626   $204.26   $204.25   $204.30  
  Purchase #2 $229.67   12.627%   $258.6704   $258.67   $258.65   $258.70  
  Purchase #3 $157.55   9.420%   $172.3912   $172.39   $172.40   $172.40  
  Purchase #4 $144.59   8.323%   $156.6242   $156.62   $156.60   $156.60  
  Purchase #5 $161.44   7.140%   $172.9668   $172.97   $172.95   $173.00  
  Purchase #6 $186.61   9.406%   $204.1625   $204.16   $204.15   $204.20  
  Purchase #7 $94.83   8.318%   $102.718   $102.72   $102.70   $102.70  
  7 purchase totals = $1,167.14       $1,271.7957   $1,271.79   $1,271.70   $1,271.90