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	$171.25	9.853%	$188.1233	$188.12	$188.10	$188.10
Purchase #2	$148.30	6.139%	$157.4041	$157.40	$157.40	$157.40
Purchase #3	$148.31	9.349%	$162.1755	$162.18	$162.20	$162.20
Purchase #4	$233.54	7.320%	$250.6351	$250.64	$250.65	$250.60
Purchase #5	$67.92	5.759%	$71.8315	$71.83	$71.85	$71.80
Purchase #6	$221.56	7.459%	$238.0862	$238.09	$238.10	$238.10
Purchase #7	$111.73	9.116%	$121.9153	$121.92	$121.90	$121.90
7 purchase totals =	$1,102.61		$1,190.1710	$1,190.18	$1,190.20	$1,190.10