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 $98.65   8.673%   $107.2059   $107.21   $107.20   $107.20  
  Purchase #2 $206.49   5.508%   $217.8635   $217.86   $217.85   $217.90  
  Purchase #3 $36.60   5.468%   $38.6013   $38.60   $38.60   $38.60  
  Purchase #4 $249.87   9.465%   $273.5202   $273.52   $273.50   $273.50  
  Purchase #5 $217.72   10.196%   $239.9187   $239.92   $239.90   $239.90  
  Purchase #6 $150.85   8.208%   $163.2318   $163.23   $163.25   $163.20  
  Purchase #7 $21.77   11.231%   $24.215   $24.22   $24.20   $24.20  
  7 purchase totals = $981.95       $1,064.5564   $1,064.56   $1,064.50   $1,064.50