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	$92.93	6.736%	$99.1898	$99.19	$99.20	$99.20
Purchase #2	$170.55	10.454%	$188.3793	$188.38	$188.40	$188.40
Purchase #3	$53.87	12.343%	$60.5192	$60.52	$60.50	$60.50
Purchase #4	$73.35	6.466%	$78.0928	$78.09	$78.10	$78.10
Purchase #5	$93.92	3.134%	$96.8635	$96.86	$96.85	$96.90
Purchase #6	$178.26	7.337%	$191.3389	$191.34	$191.35	$191.30
Purchase #7	$246.72	5.271%	$259.7246	$259.72	$259.70	$259.70
7 purchase totals =	$909.60		$974.1081	$974.10	$974.10	$974.10