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 $209.94   3.821%   $217.9618   $217.96   $217.95   $218.00  
  Purchase #2 $217.93   13.177%   $246.6466   $246.65   $246.65   $246.60  
  Purchase #3 $165.99   5.106%   $174.4654   $174.47   $174.45   $174.50  
  Purchase #4 $41.53   10.256%   $45.7893   $45.79   $45.80   $45.80  
  Purchase #5 $38.52   4.211%   $40.1421   $40.14   $40.15   $40.10  
  Purchase #6 $39.59   10.186%   $43.6226   $43.62   $43.60   $43.60  
  Purchase #7 $215.74   9.871%   $237.0357   $237.04   $237.05   $237.00  
  7 purchase totals = $929.24       $1,005.6635   $1,005.67   $1,005.65   $1,005.60