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	$41.25	9.756%	$45.2744	$45.27	$45.25	$45.30
Purchase #2	$90.64	9.529%	$99.2771	$99.28	$99.30	$99.30
Purchase #3	$27.33	13.298%	$30.9643	$30.96	$30.95	$31.00
Purchase #4	$226.66	12.374%	$254.7069	$254.71	$254.70	$254.70
Purchase #5	$166.89	12.354%	$187.5076	$187.51	$187.50	$187.50
Purchase #6	$47.99	7.377%	$51.5302	$51.53	$51.55	$51.50
Purchase #7	$108.85	7.158%	$116.6415	$116.64	$116.65	$116.60
7 purchase totals =	$709.61		$785.9020	$785.90	$785.90	$785.90