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 $67.93   9.482%   $74.3711   $74.37   $74.35   $74.40  
  Purchase #2 $174.92   13.292%   $198.1704   $198.17   $198.15   $198.20  
  Purchase #3 $23.32   9.245%   $25.4759   $25.48   $25.50   $25.50  
  Purchase #4 $236.48   11.295%   $263.1904   $263.19   $263.20   $263.20  
  Purchase #5 $73.78   4.303%   $76.9548   $76.95   $76.95   $77.00  
  Purchase #6 $59.81   6.556%   $63.7311   $63.73   $63.75   $63.70  
  Purchase #7 $64.62   9.557%   $70.7957   $70.80   $70.80   $70.80  
  7 purchase totals = $700.86       $772.6894   $772.69   $772.70   $772.80