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	$170.97	4.750%	$179.0911	$179.09	$179.10	$179.10
Purchase #2	$121.29	5.331%	$127.756	$127.76	$127.75	$127.80
Purchase #3	$57.41	3.614%	$59.4848	$59.48	$59.50	$59.50
Purchase #4	$37.84	11.492%	$42.1886	$42.19	$42.20	$42.20
Purchase #5	$92.92	5.245%	$97.7937	$97.79	$97.80	$97.80
Purchase #6	$190.31	6.155%	$202.0236	$202.02	$202.00	$202.00
Purchase #7	$237.40	10.850%	$263.1579	$263.16	$263.15	$263.20
7 purchase totals =	$908.14		$971.4957	$971.49	$971.50	$971.60