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 $60.59   9.346%   $66.2527   $66.25   $66.25   $66.30  
  Purchase #2 $216.31   7.442%   $232.4078   $232.41   $232.40   $232.40  
  Purchase #3 $44.55   6.628%   $47.5028   $47.50   $47.50   $47.50  
  Purchase #4 $48.79   7.236%   $52.3204   $52.32   $52.30   $52.30  
  Purchase #5 $159.25   13.633%   $180.9606   $180.96   $180.95   $181.00  
  Purchase #6 $242.91   10.496%   $268.4058   $268.41   $268.40   $268.40  
  Purchase #7 $93.45   5.520%   $98.6084   $98.61   $98.60   $98.60  
  7 purchase totals = $865.85       $946.4585   $946.46   $946.40   $946.50