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	$155.92	6.679%	$166.3339	$166.33	$166.35	$166.30
Purchase #2	$106.72	4.397%	$111.4125	$111.41	$111.40	$111.40
Purchase #3	$123.39	5.635%	$130.343	$130.34	$130.35	$130.30
Purchase #4	$220.79	5.664%	$233.2955	$233.30	$233.30	$233.30
Purchase #5	$162.87	3.399%	$168.406	$168.41	$168.40	$168.40
Purchase #6	$174.48	10.197%	$192.2717	$192.27	$192.25	$192.30
Purchase #7	$243.34	3.137%	$250.9736	$250.97	$250.95	$251.00
7 purchase totals =	$1,187.51		$1,253.0362	$1,253.03	$1,253.00	$1,253.00