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	$88.91	10.274%	$98.0446	$98.04	$98.05	$98.00
Purchase #2	$203.95	7.424%	$219.0912	$219.09	$219.10	$219.10
Purchase #3	$44.50	13.408%	$50.4666	$50.47	$50.45	$50.50
Purchase #4	$47.29	13.604%	$53.7233	$53.72	$53.70	$53.70
Purchase #5	$76.89	7.840%	$82.9182	$82.92	$82.90	$82.90
Purchase #6	$167.49	13.851%	$190.689	$190.69	$190.70	$190.70
Purchase #7	$93.84	6.200%	$99.6581	$99.66	$99.65	$99.70
7 purchase totals =	$722.87		$794.5910	$794.59	$794.55	$794.60