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 $39.52   4.601%   $41.3383   $41.34   $41.35   $41.30  
  Purchase #2 $91.61   4.494%   $95.727   $95.73   $95.75   $95.70  
  Purchase #3 $226.86   9.769%   $249.022   $249.02   $249.00   $249.00  
  Purchase #4 $227.26   4.701%   $237.9435   $237.94   $237.95   $237.90  
  Purchase #5 $161.93   6.534%   $172.5105   $172.51   $172.50   $172.50  
  Purchase #6 $172.97   7.486%   $185.9185   $185.92   $185.90   $185.90  
  Purchase #7 $124.53   10.780%   $137.9543   $137.95   $137.95   $138.00  
  7 purchase totals = $1,044.68       $1,120.4141   $1,120.41   $1,120.40   $1,120.30