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 $152.68   12.117%   $171.1802   $171.18   $171.20   $171.20  
  Purchase #2 $117.67   11.601%   $131.3209   $131.32   $131.30   $131.30  
  Purchase #3 $91.81   12.840%   $103.5984   $103.60   $103.60   $103.60  
  Purchase #4 $229.81   9.685%   $252.0671   $252.07   $252.05   $252.10  
  Purchase #5 $119.40   5.149%   $125.5479   $125.55   $125.55   $125.50  
  Purchase #6 $173.48   5.392%   $182.834   $182.83   $182.85   $182.80  
  Purchase #7 $116.91   8.542%   $126.8965   $126.90   $126.90   $126.90  
  7 purchase totals = $1,001.76       $1,093.4450   $1,093.45   $1,093.45   $1,093.40