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	$98.26	12.222%	$110.2693	$110.27	$110.25	$110.30
Purchase #2	$223.80	5.522%	$236.1582	$236.16	$236.15	$236.20
Purchase #3	$50.43	6.135%	$53.5239	$53.52	$53.50	$53.50
Purchase #4	$168.52	3.294%	$174.071	$174.07	$174.05	$174.10
Purchase #5	$53.86	5.474%	$56.8083	$56.81	$56.80	$56.80
Purchase #6	$52.32	10.703%	$57.9198	$57.92	$57.90	$57.90
Purchase #7	$56.54	5.874%	$59.8612	$59.86	$59.85	$59.90
7 purchase totals =	$703.73		$748.6117	$748.61	$748.50	$748.70