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	$234.86	8.533%	$254.9006	$254.90	$254.90	$254.90
Purchase #2	$152.98	7.352%	$164.2271	$164.23	$164.25	$164.20
Purchase #3	$20.46	3.549%	$21.1861	$21.19	$21.20	$21.20
Purchase #4	$170.86	8.596%	$185.5471	$185.55	$185.55	$185.50
Purchase #5	$183.73	13.152%	$207.8942	$207.89	$207.90	$207.90
Purchase #6	$168.36	11.835%	$188.2854	$188.29	$188.30	$188.30
Purchase #7	$58.52	7.289%	$62.7855	$62.79	$62.80	$62.80
7 purchase totals =	$989.77		$1,084.8260	$1,084.84	$1,084.90	$1,084.80