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	$90.34	7.256%	$96.8951	$96.90	$96.90	$96.90
Purchase #2	$77.48	4.518%	$80.9805	$80.98	$81.00	$81.00
Purchase #3	$53.39	3.808%	$55.4231	$55.42	$55.40	$55.40
Purchase #4	$50.50	3.277%	$52.1549	$52.15	$52.15	$52.20
Purchase #5	$10.75	5.171%	$11.3059	$11.31	$11.30	$11.30
Purchase #6	$196.97	12.315%	$221.2269	$221.23	$221.25	$221.20
Purchase #7	$83.56	6.385%	$88.8953	$88.90	$88.90	$88.90
7 purchase totals =	$562.99		$606.8817	$606.89	$606.90	$606.90