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 $70.52   3.552%   $73.0249   $73.02   $73.00   $73.00  
  Purchase #2 $236.94   10.164%   $261.0226   $261.02   $261.00   $261.00  
  Purchase #3 $71.71   11.339%   $79.8412   $79.84   $79.85   $79.80  
  Purchase #4 $207.35   11.237%   $230.6499   $230.65   $230.65   $230.60  
  Purchase #5 $188.76   4.405%   $197.0749   $197.07   $197.05   $197.10  
  Purchase #6 $158.91   7.205%   $170.3595   $170.36   $170.35   $170.40  
  Purchase #7 $98.37   13.708%   $111.8546   $111.85   $111.85   $111.90  
  7 purchase totals = $1,032.56       $1,123.8276   $1,123.81   $1,123.75   $1,123.80