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	$69.31	13.352%	$78.5643	$78.56	$78.55	$78.60
Purchase #2	$57.46	13.285%	$65.0936	$65.09	$65.10	$65.10
Purchase #3	$71.88	11.518%	$80.1591	$80.16	$80.15	$80.20
Purchase #4	$61.76	3.586%	$63.9747	$63.97	$63.95	$64.00
Purchase #5	$185.89	4.832%	$194.8722	$194.87	$194.85	$194.90
Purchase #6	$170.43	6.265%	$181.1074	$181.11	$181.10	$181.10
Purchase #7	$223.96	10.296%	$247.0189	$247.02	$247.00	$247.00
7 purchase totals =	$840.69		$910.7902	$910.78	$910.70	$910.90