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 $208.31   10.227%   $229.6139   $229.61   $229.60   $229.60  
  Purchase #2 $44.82   3.782%   $46.5151   $46.52   $46.50   $46.50  
  Purchase #3 $180.76   3.167%   $186.4847   $186.48   $186.50   $186.50  
  Purchase #4 $105.48   11.453%   $117.5606   $117.56   $117.55   $117.60  
  Purchase #5 $187.60   7.199%   $201.1053   $201.11   $201.10   $201.10  
  Purchase #6 $198.91   5.192%   $209.2374   $209.24   $209.25   $209.20  
  Purchase #7 $26.52   13.513%   $30.1036   $30.10   $30.10   $30.10  
  7 purchase totals = $952.40       $1,020.6206   $1,020.62   $1,020.60   $1,020.60