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	$6.47	4.405%	$6.755	$6.76	$6.75	$6.80
Purchase #2	$105.54	6.538%	$112.4402	$112.44	$112.45	$112.40
Purchase #3	$114.54	3.224%	$118.2328	$118.23	$118.25	$118.20
Purchase #4	$140.71	8.580%	$152.7829	$152.78	$152.80	$152.80
Purchase #5	$236.38	11.855%	$264.4028	$264.40	$264.40	$264.40
Purchase #6	$213.92	7.259%	$229.4485	$229.45	$229.45	$229.40
Purchase #7	$66.28	7.640%	$71.3438	$71.34	$71.35	$71.30
7 purchase totals =	$883.84		$955.4060	$955.40	$955.45	$955.30