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 $172.62   11.726%   $192.8614   $192.86   $192.85   $192.90  
  Purchase #2 $241.62   5.370%   $254.595   $254.60   $254.60   $254.60  
  Purchase #3 $67.42   5.552%   $71.1632   $71.16   $71.15   $71.20  
  Purchase #4 $250.79   11.108%   $278.6478   $278.65   $278.65   $278.60  
  Purchase #5 $141.74   12.124%   $158.9246   $158.92   $158.90   $158.90  
  Purchase #6 $211.97   11.318%   $235.9608   $235.96   $235.95   $236.00  
  Purchase #7 $208.89   9.768%   $229.2944   $229.29   $229.30   $229.30  
  7 purchase totals = $1,295.05       $1,421.4472   $1,421.44   $1,421.40   $1,421.50