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 $51.71   12.529%   $58.1887   $58.19   $58.20   $58.20  
  Purchase #2 $220.63   9.373%   $241.3096   $241.31   $241.30   $241.30  
  Purchase #3 $56.35   8.857%   $61.3409   $61.34   $61.35   $61.30  
  Purchase #4 $237.66   9.737%   $260.801   $260.80   $260.80   $260.80  
  Purchase #5 $247.69   12.429%   $278.4754   $278.48   $278.50   $278.50  
  Purchase #6 $34.96   11.240%   $38.8895   $38.89   $38.90   $38.90  
  Purchase #7 $122.34   12.135%   $137.186   $137.19   $137.20   $137.20  
  7 purchase totals = $971.34       $1,076.1911   $1,076.20   $1,076.25   $1,076.20