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	$35.74	6.753%	$38.1535	$38.15	$38.15	$38.20
Purchase #2	$191.61	3.723%	$198.7436	$198.74	$198.75	$198.70
Purchase #3	$73.57	9.433%	$80.5099	$80.51	$80.50	$80.50
Purchase #4	$244.37	12.687%	$275.3732	$275.37	$275.35	$275.40
Purchase #5	$198.33	9.805%	$217.7763	$217.78	$217.80	$217.80
Purchase #6	$153.40	11.336%	$170.7894	$170.79	$170.80	$170.80
Purchase #7	$104.73	6.850%	$111.904	$111.90	$111.90	$111.90
7 purchase totals =	$1,001.75		$1,093.2499	$1,093.24	$1,093.25	$1,093.30