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	$88.38	4.670%	$92.5073	$92.51	$92.50	$92.50
Purchase #2	$143.36	10.418%	$158.2952	$158.30	$158.30	$158.30
Purchase #3	$50.85	12.489%	$57.2007	$57.20	$57.20	$57.20
Purchase #4	$127.70	4.529%	$133.4835	$133.48	$133.50	$133.50
Purchase #5	$183.67	4.253%	$191.4815	$191.48	$191.50	$191.50
Purchase #6	$191.43	4.217%	$199.5026	$199.50	$199.50	$199.50
Purchase #7	$86.43	3.308%	$89.2891	$89.29	$89.30	$89.30
7 purchase totals =	$871.82		$921.7599	$921.76	$921.80	$921.80