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	$170.40	4.781%	$178.5468	$178.55	$178.55	$178.50
Purchase #2	$39.73	11.300%	$44.2195	$44.22	$44.20	$44.20
Purchase #3	$108.48	6.767%	$115.8208	$115.82	$115.80	$115.80
Purchase #4	$87.37	3.562%	$90.4821	$90.48	$90.50	$90.50
Purchase #5	$19.52	3.514%	$20.2059	$20.21	$20.20	$20.20
Purchase #6	$90.36	6.124%	$95.8936	$95.89	$95.90	$95.90
Purchase #7	$194.86	7.794%	$210.0474	$210.05	$210.05	$210.00
7 purchase totals =	$710.72		$755.2161	$755.22	$755.20	$755.10