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	$89.28	10.119%	$98.3142	$98.31	$98.30	$98.30
Purchase #2	$78.34	10.716%	$86.7349	$86.73	$86.75	$86.70
Purchase #3	$73.73	6.371%	$78.4273	$78.43	$78.45	$78.40
Purchase #4	$15.42	13.764%	$17.5424	$17.54	$17.55	$17.50
Purchase #5	$172.33	11.132%	$191.5138	$191.51	$191.50	$191.50
Purchase #6	$228.49	7.629%	$245.9215	$245.92	$245.90	$245.90
Purchase #7	$63.61	9.646%	$69.7458	$69.75	$69.75	$69.70
7 purchase totals =	$721.20		$788.1999	$788.19	$788.20	$788.00