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 $218.91   12.467%   $246.2015   $246.20   $246.20   $246.20  
  Purchase #2 $153.68   11.283%   $171.0197   $171.02   $171.00   $171.00  
  Purchase #3 $146.36   13.823%   $166.5913   $166.59   $166.60   $166.60  
  Purchase #4 $226.81   9.705%   $248.8219   $248.82   $248.80   $248.80  
  Purchase #5 $121.82   5.831%   $128.9233   $128.92   $128.90   $128.90  
  Purchase #6 $224.63   4.855%   $235.5358   $235.54   $235.55   $235.50  
  Purchase #7 $60.90   13.783%   $69.2938   $69.29   $69.30   $69.30  
  7 purchase totals = $1,153.11       $1,266.3873   $1,266.38   $1,266.35   $1,266.30