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	$154.35	7.704%	$166.2411	$166.24	$166.25	$166.20
Purchase #2	$95.69	3.813%	$99.3387	$99.34	$99.35	$99.30
Purchase #3	$187.45	12.172%	$210.2664	$210.27	$210.25	$210.30
Purchase #4	$47.69	5.375%	$50.2533	$50.25	$50.25	$50.30
Purchase #5	$217.73	7.837%	$234.7935	$234.79	$234.80	$234.80
Purchase #6	$176.42	6.633%	$188.1219	$188.12	$188.10	$188.10
Purchase #7	$130.91	7.680%	$140.9639	$140.96	$140.95	$141.00
7 purchase totals =	$1,010.24		$1,089.9788	$1,089.97	$1,089.95	$1,090.00