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	$91.99	7.791%	$99.1569	$99.16	$99.15	$99.20
Purchase #2	$175.44	6.173%	$186.2699	$186.27	$186.25	$186.30
Purchase #3	$115.62	11.122%	$128.4793	$128.48	$128.50	$128.50
Purchase #4	$174.89	4.727%	$183.1571	$183.16	$183.15	$183.20
Purchase #5	$39.54	7.461%	$42.4901	$42.49	$42.50	$42.50
Purchase #6	$235.99	5.297%	$248.4904	$248.49	$248.50	$248.50
Purchase #7	$59.81	13.230%	$67.7229	$67.72	$67.70	$67.70
7 purchase totals =	$893.28		$955.7666	$955.77	$955.75	$955.90