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	$85.85	5.781%	$90.813	$90.81	$90.80	$90.80
Purchase #2	$162.42	12.146%	$182.1475	$182.15	$182.15	$182.10
Purchase #3	$101.79	11.821%	$113.8226	$113.82	$113.80	$113.80
Purchase #4	$170.32	9.820%	$187.0454	$187.05	$187.05	$187.00
Purchase #5	$148.90	7.570%	$160.1717	$160.17	$160.15	$160.20
Purchase #6	$133.66	12.266%	$150.0547	$150.05	$150.05	$150.10
Purchase #7	$183.59	11.402%	$204.5229	$204.52	$204.50	$204.50
7 purchase totals =	$986.53		$1,088.5778	$1,088.57	$1,088.50	$1,088.50