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 $232.26   13.625%   $263.9054   $263.91   $263.90   $263.90  
  Purchase #2 $79.47   10.538%   $87.8445   $87.84   $87.85   $87.80  
  Purchase #3 $70.56   7.796%   $76.0609   $76.06   $76.05   $76.10  
  Purchase #4 $68.45   13.809%   $77.9023   $77.90   $77.90   $77.90  
  Purchase #5 $195.92   13.391%   $222.1556   $222.16   $222.15   $222.20  
  Purchase #6 $242.34   12.347%   $272.2617   $272.26   $272.25   $272.30  
  Purchase #7 $173.58   9.542%   $190.143   $190.14   $190.15   $190.10  
  7 purchase totals = $1,062.58       $1,190.2734   $1,190.27   $1,190.25   $1,190.30