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 $105.86   13.531%   $120.1839   $120.18   $120.20   $120.20  
  Purchase #2 $239.88   11.118%   $266.5499   $266.55   $266.55   $266.50  
  Purchase #3 $199.66   9.579%   $218.7854   $218.79   $218.80   $218.80  
  Purchase #4 $240.37   13.814%   $273.5747   $273.57   $273.55   $273.60  
  Purchase #5 $142.39   3.435%   $147.2811   $147.28   $147.30   $147.30  
  Purchase #6 $241.30   5.612%   $254.8418   $254.84   $254.85   $254.80  
  Purchase #7 $177.55   3.337%   $183.4748   $183.47   $183.45   $183.50  
  7 purchase totals = $1,347.01       $1,464.6916   $1,464.68   $1,464.70   $1,464.70