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	$242.86	13.342%	$275.2624	$275.26	$275.25	$275.30
Purchase #2	$167.94	13.667%	$190.8924	$190.89	$190.90	$190.90
Purchase #3	$208.73	12.228%	$234.2535	$234.25	$234.25	$234.30
Purchase #4	$146.79	6.729%	$156.6675	$156.67	$156.65	$156.70
Purchase #5	$62.78	6.179%	$66.6592	$66.66	$66.65	$66.70
Purchase #6	$106.36	4.279%	$110.9111	$110.91	$110.90	$110.90
Purchase #7	$101.47	9.280%	$110.8864	$110.89	$110.90	$110.90
7 purchase totals =	$1,036.93		$1,145.5325	$1,145.53	$1,145.50	$1,145.70