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 $176.89   12.583%   $199.1481   $199.15   $199.15   $199.10  
  Purchase #2 $224.54   9.380%   $245.6019   $245.60   $245.60   $245.60  
  Purchase #3 $219.42   12.794%   $247.4926   $247.49   $247.50   $247.50  
  Purchase #4 $54.60   12.408%   $61.3748   $61.37   $61.35   $61.40  
  Purchase #5 $81.54   13.184%   $92.2902   $92.29   $92.30   $92.30  
  Purchase #6 $201.87   9.626%   $221.302   $221.30   $221.30   $221.30  
  Purchase #7 $20.72   8.401%   $22.4607   $22.46   $22.45   $22.50  
  7 purchase totals = $979.58       $1,089.6703   $1,089.66   $1,089.65   $1,089.70