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	$25.41	7.241%	$27.2499	$27.25	$27.25	$27.20
Purchase #2	$77.82	9.506%	$85.2176	$85.22	$85.20	$85.20
Purchase #3	$149.84	9.260%	$163.7152	$163.72	$163.70	$163.70
Purchase #4	$119.63	10.252%	$131.8945	$131.89	$131.90	$131.90
Purchase #5	$6.49	10.728%	$7.1862	$7.19	$7.20	$7.20
Purchase #6	$98.73	12.493%	$111.0643	$111.06	$111.05	$111.10
Purchase #7	$57.45	6.367%	$61.1078	$61.11	$61.10	$61.10
7 purchase totals =	$535.37		$587.4355	$587.44	$587.40	$587.40