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 $168.40   7.635%   $181.2573   $181.26   $181.25   $181.30  
  Purchase #2 $126.91   5.591%   $134.0055   $134.01   $134.00   $134.00  
  Purchase #3 $53.30   9.511%   $58.3694   $58.37   $58.35   $58.40  
  Purchase #4 $244.30   3.804%   $253.5932   $253.59   $253.60   $253.60  
  Purchase #5 $134.25   6.508%   $142.987   $142.99   $143.00   $143.00  
  Purchase #6 $58.38   10.211%   $64.3412   $64.34   $64.35   $64.30  
  Purchase #7 $226.34   6.404%   $240.8348   $240.83   $240.85   $240.80  
  7 purchase totals = $1,011.88       $1,075.3884   $1,075.39   $1,075.40   $1,075.40