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 $126.97   12.564%   $142.9225   $142.92   $142.90   $142.90  
  Purchase #2 $129.54   10.153%   $142.6922   $142.69   $142.70   $142.70  
  Purchase #3 $106.63   13.587%   $121.1178   $121.12   $121.10   $121.10  
  Purchase #4 $152.64   10.553%   $168.7481   $168.75   $168.75   $168.70  
  Purchase #5 $223.52   4.209%   $232.928   $232.93   $232.95   $232.90  
  Purchase #6 $76.54   11.579%   $85.4026   $85.40   $85.40   $85.40  
  Purchase #7 $165.57   10.499%   $182.9532   $182.95   $182.95   $183.00  
  7 purchase totals = $981.41       $1,076.7644   $1,076.76   $1,076.75   $1,076.70