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 $112.57   12.538%   $126.684   $126.68   $126.70   $126.70  
  Purchase #2 $124.32   7.112%   $133.1616   $133.16   $133.15   $133.20  
  Purchase #3 $228.68   5.166%   $240.4936   $240.49   $240.50   $240.50  
  Purchase #4 $71.26   3.584%   $73.814   $73.81   $73.80   $73.80  
  Purchase #5 $101.42   4.617%   $106.1026   $106.10   $106.10   $106.10  
  Purchase #6 $125.81   6.748%   $134.2997   $134.30   $134.30   $134.30  
  Purchase #7 $179.60   13.239%   $203.3772   $203.38   $203.40   $203.40  
  7 purchase totals = $943.66       $1,017.9327   $1,017.92   $1,017.95   $1,018.00