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 $111.71   12.868%   $126.0848   $126.08   $126.10   $126.10  
  Purchase #2 $169.55   3.216%   $175.0027   $175.00   $175.00   $175.00  
  Purchase #3 $196.82   8.278%   $213.1128   $213.11   $213.10   $213.10  
  Purchase #4 $78.94   12.659%   $88.933   $88.93   $88.95   $88.90  
  Purchase #5 $250.95   4.560%   $262.3933   $262.39   $262.40   $262.40  
  Purchase #6 $205.90   11.535%   $229.6506   $229.65   $229.65   $229.70  
  Purchase #7 $122.43   6.746%   $130.6891   $130.69   $130.70   $130.70  
  7 purchase totals = $1,136.30       $1,225.8663   $1,225.85   $1,225.90   $1,225.90