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 $213.84   5.799%   $226.2406   $226.24   $226.25   $226.20  
  Purchase #2 $60.50   6.717%   $64.5638   $64.56   $64.55   $64.60  
  Purchase #3 $198.59   8.516%   $215.5019   $215.50   $215.50   $215.50  
  Purchase #4 $91.92   12.191%   $103.126   $103.13   $103.15   $103.10  
  Purchase #5 $130.62   8.575%   $141.8207   $141.82   $141.80   $141.80  
  Purchase #6 $166.98   11.859%   $186.7822   $186.78   $186.80   $186.80  
  Purchase #7 $88.78   3.249%   $91.6645   $91.66   $91.65   $91.70  
  7 purchase totals = $951.23       $1,029.6997   $1,029.69   $1,029.70   $1,029.70