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	$125.55	10.844%	$139.1646	$139.16	$139.15	$139.20
Purchase #2	$20.51	9.645%	$22.4882	$22.49	$22.50	$22.50
Purchase #3	$115.87	13.271%	$131.2471	$131.25	$131.25	$131.20
Purchase #4	$92.84	7.874%	$100.1502	$100.15	$100.15	$100.20
Purchase #5	$148.97	13.760%	$169.4683	$169.47	$169.45	$169.50
Purchase #6	$232.34	11.117%	$258.1692	$258.17	$258.15	$258.20
Purchase #7	$181.72	10.295%	$200.4281	$200.43	$200.45	$200.40
7 purchase totals =	$917.80		$1,021.1157	$1,021.12	$1,021.10	$1,021.20