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	$94.36	5.851%	$99.881	$99.88	$99.90	$99.90
Purchase #2	$6.75	7.592%	$7.2625	$7.26	$7.25	$7.30
Purchase #3	$30.72	6.533%	$32.7269	$32.73	$32.75	$32.70
Purchase #4	$131.38	4.194%	$136.8901	$136.89	$136.90	$136.90
Purchase #5	$110.91	9.175%	$121.086	$121.09	$121.10	$121.10
Purchase #6	$201.52	3.745%	$209.0669	$209.07	$209.05	$209.10
Purchase #7	$218.39	12.139%	$244.9004	$244.90	$244.90	$244.90
7 purchase totals =	$794.03		$851.8138	$851.82	$851.85	$851.90