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	$50.62	3.279%	$52.2798	$52.28	$52.30	$52.30
Purchase #2	$105.83	9.355%	$115.7304	$115.73	$115.75	$115.70
Purchase #3	$180.78	5.586%	$190.8784	$190.88	$190.90	$190.90
Purchase #4	$93.57	6.357%	$99.5182	$99.52	$99.50	$99.50
Purchase #5	$91.53	7.186%	$98.1073	$98.11	$98.10	$98.10
Purchase #6	$245.36	12.536%	$276.1183	$276.12	$276.10	$276.10
Purchase #7	$58.98	12.787%	$66.5218	$66.52	$66.50	$66.50
7 purchase totals =	$826.67		$899.1542	$899.16	$899.15	$899.10