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	$113.93	8.587%	$123.7132	$123.71	$123.70	$123.70
Purchase #2	$82.41	9.659%	$90.37	$90.37	$90.35	$90.40
Purchase #3	$145.37	3.261%	$150.1105	$150.11	$150.10	$150.10
Purchase #4	$7.83	3.400%	$8.0962	$8.10	$8.10	$8.10
Purchase #5	$34.33	6.574%	$36.5869	$36.59	$36.60	$36.60
Purchase #6	$63.48	13.281%	$71.9108	$71.91	$71.90	$71.90
Purchase #7	$86.35	3.282%	$89.184	$89.18	$89.20	$89.20
7 purchase totals =	$533.70		$569.9716	$569.97	$569.95	$570.00