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	$198.88	8.296%	$215.3791	$215.38	$215.40	$215.40
Purchase #2	$84.97	7.761%	$91.5645	$91.56	$91.55	$91.60
Purchase #3	$101.69	12.380%	$114.2792	$114.28	$114.30	$114.30
Purchase #4	$42.90	4.621%	$44.8824	$44.88	$44.90	$44.90
Purchase #5	$124.27	12.824%	$140.2064	$140.21	$140.20	$140.20
Purchase #6	$136.36	3.231%	$140.7658	$140.77	$140.75	$140.80
Purchase #7	$40.81	3.803%	$42.362	$42.36	$42.35	$42.40
7 purchase totals =	$729.88		$789.4394	$789.44	$789.45	$789.60