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 $9.68   4.380%   $10.104   $10.10   $10.10   $10.10  
  Purchase #2 $127.67   13.182%   $144.4995   $144.50   $144.50   $144.50  
  Purchase #3 $217.39   9.106%   $237.1855   $237.19   $237.20   $237.20  
  Purchase #4 $197.78   10.270%   $218.092   $218.09   $218.10   $218.10  
  Purchase #5 $84.72   3.727%   $87.8775   $87.88   $87.90   $87.90  
  Purchase #6 $229.46   12.302%   $257.6882   $257.69   $257.70   $257.70  
  Purchase #7 $243.55   6.633%   $259.7047   $259.70   $259.70   $259.70  
  7 purchase totals = $1,110.25       $1,215.1514   $1,215.15   $1,215.20   $1,215.20