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 $208.25   8.564%   $226.0845   $226.08   $226.10   $226.10  
  Purchase #2 $181.99   5.261%   $191.5645   $191.56   $191.55   $191.60  
  Purchase #3 $66.57   10.712%   $73.701   $73.70   $73.70   $73.70  
  Purchase #4 $177.99   3.730%   $184.629   $184.63   $184.65   $184.60  
  Purchase #5 $211.37   9.548%   $231.5516   $231.55   $231.55   $231.60  
  Purchase #6 $130.57   10.760%   $144.6193   $144.62   $144.60   $144.60  
  Purchase #7 $8.54   9.516%   $9.3527   $9.35   $9.35   $9.40  
  7 purchase totals = $985.28       $1,061.5026   $1,061.49   $1,061.50   $1,061.60