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	$26.94	12.484%	$30.3032	$30.30	$30.30	$30.30
Purchase #2	$179.86	9.257%	$196.5096	$196.51	$196.50	$196.50
Purchase #3	$84.96	7.287%	$91.151	$91.15	$91.15	$91.20
Purchase #4	$215.36	10.655%	$238.3066	$238.31	$238.30	$238.30
Purchase #5	$23.32	6.272%	$24.7826	$24.78	$24.80	$24.80
Purchase #6	$168.75	11.711%	$188.5123	$188.51	$188.50	$188.50
Purchase #7	$111.75	11.599%	$124.7119	$124.71	$124.70	$124.70
7 purchase totals =	$810.94		$894.2772	$894.27	$894.25	$894.30