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	$71.89	6.732%	$76.7296	$76.73	$76.75	$76.70
Purchase #2	$179.47	9.515%	$196.5466	$196.55	$196.55	$196.50
Purchase #3	$167.79	12.226%	$188.304	$188.30	$188.30	$188.30
Purchase #4	$177.47	7.140%	$190.1414	$190.14	$190.15	$190.10
Purchase #5	$45.93	11.189%	$51.0691	$51.07	$51.05	$51.10
Purchase #6	$51.95	8.408%	$56.318	$56.32	$56.30	$56.30
Purchase #7	$139.87	12.800%	$157.7734	$157.77	$157.75	$157.80
7 purchase totals =	$834.37		$916.8821	$916.88	$916.85	$916.80