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 $190.79   13.406%   $216.3673   $216.37   $216.35   $216.40  
  Purchase #2 $248.86   5.492%   $262.5274   $262.53   $262.55   $262.50  
  Purchase #3 $130.39   8.748%   $141.7965   $141.80   $141.80   $141.80  
  Purchase #4 $70.25   4.712%   $73.5602   $73.56   $73.55   $73.60  
  Purchase #5 $137.52   11.613%   $153.4902   $153.49   $153.50   $153.50  
  Purchase #6 $180.39   3.272%   $186.2924   $186.29   $186.30   $186.30  
  Purchase #7 $56.69   13.234%   $64.1924   $64.19   $64.20   $64.20  
  7 purchase totals = $1,014.89       $1,098.2264   $1,098.23   $1,098.25   $1,098.30