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	$242.98	12.566%	$273.5129	$273.51	$273.50	$273.50
Purchase #2	$177.58	10.806%	$196.7693	$196.77	$196.75	$196.80
Purchase #3	$139.38	10.148%	$153.5243	$153.52	$153.50	$153.50
Purchase #4	$224.54	8.290%	$243.1544	$243.15	$243.15	$243.20
Purchase #5	$45.88	7.833%	$49.4738	$49.47	$49.45	$49.50
Purchase #6	$81.85	13.813%	$93.1559	$93.16	$93.15	$93.20
Purchase #7	$36.63	5.232%	$38.5465	$38.55	$38.55	$38.50
7 purchase totals =	$948.84		$1,048.1371	$1,048.13	$1,048.05	$1,048.20