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 $136.39   12.659%   $153.6556   $153.66   $153.65   $153.70  
  Purchase #2 $98.88   3.789%   $102.6266   $102.63   $102.65   $102.60  
  Purchase #3 $87.53   6.829%   $93.5074   $93.51   $93.50   $93.50  
  Purchase #4 $208.40   3.226%   $215.123   $215.12   $215.10   $215.10  
  Purchase #5 $240.35   13.565%   $272.9535   $272.95   $272.95   $273.00  
  Purchase #6 $42.46   7.368%   $45.5885   $45.59   $45.60   $45.60  
  Purchase #7 $234.76   4.846%   $246.1365   $246.14   $246.15   $246.10  
  7 purchase totals = $1,048.77       $1,129.5911   $1,129.60   $1,129.60   $1,129.60