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	$195.94	7.171%	$209.9909	$209.99	$210.00	$210.00
Purchase #2	$135.38	12.550%	$152.3702	$152.37	$152.35	$152.40
Purchase #3	$113.52	3.389%	$117.3672	$117.37	$117.35	$117.40
Purchase #4	$119.45	9.753%	$131.1	$131.10	$131.10	$131.10
Purchase #5	$54.60	9.521%	$59.7985	$59.80	$59.80	$59.80
Purchase #6	$77.31	7.206%	$82.881	$82.88	$82.90	$82.90
Purchase #7	$87.51	4.117%	$91.1128	$91.11	$91.10	$91.10
7 purchase totals =	$783.71		$844.6206	$844.62	$844.60	$844.70