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	$70.62	13.507%	$80.1586	$80.16	$80.15	$80.20
Purchase #2	$165.47	10.162%	$182.2851	$182.29	$182.30	$182.30
Purchase #3	$99.57	4.373%	$103.9242	$103.92	$103.90	$103.90
Purchase #4	$97.81	3.499%	$101.2324	$101.23	$101.25	$101.20
Purchase #5	$146.69	6.623%	$156.4053	$156.41	$156.40	$156.40
Purchase #6	$203.74	3.818%	$211.5188	$211.52	$211.50	$211.50
Purchase #7	$201.76	11.656%	$225.2771	$225.28	$225.30	$225.30
7 purchase totals =	$985.66		$1,060.8015	$1,060.81	$1,060.80	$1,060.80