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	$227.90	11.568%	$254.2635	$254.26	$254.25	$254.30
Purchase #2	$37.76	6.140%	$40.0785	$40.08	$40.10	$40.10
Purchase #3	$52.89	4.706%	$55.379	$55.38	$55.40	$55.40
Purchase #4	$167.31	7.171%	$179.3078	$179.31	$179.30	$179.30
Purchase #5	$75.40	4.768%	$78.9951	$79.00	$79.00	$79.00
Purchase #6	$235.82	3.710%	$244.5689	$244.57	$244.55	$244.60
Purchase #7	$41.72	6.138%	$44.2808	$44.28	$44.30	$44.30
7 purchase totals =	$838.80		$896.8736	$896.88	$896.90	$897.00