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 $116.83   6.246%   $124.1272   $124.13   $124.15   $124.10  
  Purchase #2 $17.34   10.709%   $19.1969   $19.20   $19.20   $19.20  
  Purchase #3 $134.58   5.776%   $142.3533   $142.35   $142.35   $142.40  
  Purchase #4 $111.98   5.102%   $117.6932   $117.69   $117.70   $117.70  
  Purchase #5 $239.79   4.283%   $250.0602   $250.06   $250.05   $250.10  
  Purchase #6 $88.65   11.677%   $99.0017   $99.00   $99.00   $99.00  
  Purchase #7 $181.66   6.869%   $194.1382   $194.14   $194.15   $194.10  
  7 purchase totals = $890.83       $946.5707   $946.57   $946.60   $946.60