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 $208.52   13.119%   $235.8757   $235.88   $235.90   $235.90  
  Purchase #2 $139.49   11.669%   $155.7671   $155.77   $155.75   $155.80  
  Purchase #3 $114.46   6.551%   $121.9583   $121.96   $121.95   $122.00  
  Purchase #4 $133.66   11.417%   $148.92   $148.92   $148.90   $148.90  
  Purchase #5 $5.66   3.807%   $5.8755   $5.88   $5.90   $5.90  
  Purchase #6 $120.68   3.569%   $124.9871   $124.99   $125.00   $125.00  
  Purchase #7 $93.47   5.562%   $98.6688   $98.67   $98.65   $98.70  
  7 purchase totals = $815.94       $892.0525   $892.07   $892.05   $892.20