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 $209.53   10.283%   $231.076   $231.08   $231.10   $231.10  
  Purchase #2 $187.44   7.632%   $201.7454   $201.75   $201.75   $201.70  
  Purchase #3 $52.49   4.298%   $54.746   $54.75   $54.75   $54.70  
  Purchase #4 $118.63   10.473%   $131.0541   $131.05   $131.05   $131.10  
  Purchase #5 $112.25   4.602%   $117.4157   $117.42   $117.40   $117.40  
  Purchase #6 $188.64   8.177%   $204.0651   $204.07   $204.05   $204.10  
  Purchase #7 $95.65   8.202%   $103.4952   $103.50   $103.50   $103.50  
  7 purchase totals = $964.63       $1,043.5975   $1,043.62   $1,043.60   $1,043.60