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 $176.34   12.115%   $197.7036   $197.70   $197.70   $197.70  
  Purchase #2 $9.70   3.557%   $10.045   $10.05   $10.05   $10.00  
  Purchase #3 $26.63   9.105%   $29.0547   $29.05   $29.05   $29.10  
  Purchase #4 $116.78   5.831%   $123.5894   $123.59   $123.60   $123.60  
  Purchase #5 $102.65   9.314%   $112.2108   $112.21   $112.20   $112.20  
  Purchase #6 $188.27   4.675%   $197.0716   $197.07   $197.05   $197.10  
  Purchase #7 $240.74   5.736%   $254.5488   $254.55   $254.55   $254.50  
  7 purchase totals = $861.11       $924.2239   $924.22   $924.20   $924.20