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 $17.57   11.280%   $19.5519   $19.55   $19.55   $19.60  
  Purchase #2 $125.72   4.467%   $131.3359   $131.34   $131.35   $131.30  
  Purchase #3 $191.39   12.696%   $215.6889   $215.69   $215.70   $215.70  
  Purchase #4 $49.70   5.469%   $52.4181   $52.42   $52.40   $52.40  
  Purchase #5 $245.58   9.583%   $269.1139   $269.11   $269.10   $269.10  
  Purchase #6 $236.92   5.789%   $250.6353   $250.64   $250.65   $250.60  
  Purchase #7 $88.79   8.383%   $96.2333   $96.23   $96.25   $96.20  
  7 purchase totals = $955.67       $1,034.9773   $1,034.98   $1,035.00   $1,034.90