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 $121.44   4.275%   $126.6316   $126.63   $126.65   $126.60  
  Purchase #2 $175.97   4.455%   $183.8095   $183.81   $183.80   $183.80  
  Purchase #3 $156.35   3.208%   $161.3657   $161.37   $161.35   $161.40  
  Purchase #4 $242.76   8.447%   $263.2659   $263.27   $263.25   $263.30  
  Purchase #5 $176.98   3.676%   $183.4858   $183.49   $183.50   $183.50  
  Purchase #6 $88.87   11.413%   $99.0127   $99.01   $99.00   $99.00  
  Purchase #7 $225.44   8.783%   $245.2404   $245.24   $245.25   $245.20  
  7 purchase totals = $1,187.81       $1,262.8116   $1,262.82   $1,262.80   $1,262.80