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 $231.82   6.206%   $246.2067   $246.21   $246.20   $246.20  
  Purchase #2 $169.55   3.411%   $175.3334   $175.33   $175.35   $175.30  
  Purchase #3 $147.57   7.353%   $158.4208   $158.42   $158.40   $158.40  
  Purchase #4 $189.99   8.786%   $206.6825   $206.68   $206.70   $206.70  
  Purchase #5 $209.77   6.409%   $223.2142   $223.21   $223.20   $223.20  
  Purchase #6 $225.93   6.509%   $240.6358   $240.64   $240.65   $240.60  
  Purchase #7 $240.43   11.325%   $267.6587   $267.66   $267.65   $267.70  
  7 purchase totals = $1,415.06       $1,518.1521   $1,518.15   $1,518.15   $1,518.10