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 $120.82   3.490%   $125.0366   $125.04   $125.05   $125.00  
  Purchase #2 $111.69   10.714%   $123.6565   $123.66   $123.65   $123.70  
  Purchase #3 $238.71   3.864%   $247.9338   $247.93   $247.95   $247.90  
  Purchase #4 $127.54   12.637%   $143.6572   $143.66   $143.65   $143.70  
  Purchase #5 $198.37   6.781%   $211.8215   $211.82   $211.80   $211.80  
  Purchase #6 $240.30   5.860%   $254.3816   $254.38   $254.40   $254.40  
  Purchase #7 $14.56   4.188%   $15.1698   $15.17   $15.15   $15.20  
  7 purchase totals = $1,051.99       $1,121.6570   $1,121.66   $1,121.65   $1,121.70