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	$206.87	9.380%	$226.2744	$226.27	$226.25	$226.30
Purchase #2	$161.92	6.780%	$172.8982	$172.90	$172.90	$172.90
Purchase #3	$223.79	7.375%	$240.2945	$240.29	$240.30	$240.30
Purchase #4	$52.99	7.363%	$56.8917	$56.89	$56.90	$56.90
Purchase #5	$37.49	12.861%	$42.3116	$42.31	$42.30	$42.30
Purchase #6	$229.97	7.280%	$246.7118	$246.71	$246.70	$246.70
Purchase #7	$170.56	9.591%	$186.9184	$186.92	$186.90	$186.90
7 purchase totals =	$1,083.59		$1,172.3006	$1,172.29	$1,172.25	$1,172.30