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	$27.88	3.361%	$28.817	$28.82	$28.80	$28.80
Purchase #2	$158.33	5.620%	$167.2281	$167.23	$167.25	$167.20
Purchase #3	$152.56	12.843%	$172.1533	$172.15	$172.15	$172.20
Purchase #4	$240.67	8.693%	$261.5914	$261.59	$261.60	$261.60
Purchase #5	$225.56	6.811%	$240.9229	$240.92	$240.90	$240.90
Purchase #6	$33.91	8.291%	$36.7215	$36.72	$36.70	$36.70
Purchase #7	$141.29	5.330%	$148.8208	$148.82	$148.80	$148.80
7 purchase totals =	$980.20		$1,056.2550	$1,056.25	$1,056.20	$1,056.20