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 $81.26   5.297%   $85.5643   $85.56   $85.55   $85.60  
  Purchase #2 $206.90   11.806%   $231.3266   $231.33   $231.35   $231.30  
  Purchase #3 $166.35   12.159%   $186.5765   $186.58   $186.60   $186.60  
  Purchase #4 $12.76   13.450%   $14.4762   $14.48   $14.50   $14.50  
  Purchase #5 $221.67   10.603%   $245.1737   $245.17   $245.15   $245.20  
  Purchase #6 $59.76   5.186%   $62.8592   $62.86   $62.85   $62.90  
  Purchase #7 $194.62   8.812%   $211.7699   $211.77   $211.75   $211.80  
  7 purchase totals = $943.32       $1,037.7464   $1,037.75   $1,037.75   $1,037.90