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 $212.62   12.801%   $239.8375   $239.84   $239.85   $239.80  
  Purchase #2 $194.80   5.407%   $205.3328   $205.33   $205.35   $205.30  
  Purchase #3 $60.34   13.752%   $68.638   $68.64   $68.65   $68.60  
  Purchase #4 $179.84   8.403%   $194.952   $194.95   $194.95   $195.00  
  Purchase #5 $138.65   9.144%   $151.3282   $151.33   $151.35   $151.30  
  Purchase #6 $33.67   8.527%   $36.541   $36.54   $36.55   $36.50  
  Purchase #7 $109.61   9.419%   $119.9342   $119.93   $119.95   $119.90  
  7 purchase totals = $929.53       $1,016.5637   $1,016.56   $1,016.65   $1,016.40