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 $183.42   5.574%   $193.6438   $193.64   $193.65   $193.60  
  Purchase #2 $192.65   10.391%   $212.6683   $212.67   $212.65   $212.70  
  Purchase #3 $87.51   11.605%   $97.6655   $97.67   $97.65   $97.70  
  Purchase #4 $53.71   3.303%   $55.484   $55.48   $55.50   $55.50  
  Purchase #5 $140.89   13.392%   $159.758   $159.76   $159.75   $159.80  
  Purchase #6 $16.97   10.224%   $18.705   $18.71   $18.70   $18.70  
  Purchase #7 $221.49   5.417%   $233.4881   $233.49   $233.50   $233.50  
  7 purchase totals = $896.64       $971.4127   $971.42   $971.40   $971.50