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	$64.70	12.803%	$72.9835	$72.98	$73.00	$73.00
Purchase #2	$26.38	9.298%	$28.8328	$28.83	$28.85	$28.80
Purchase #3	$32.38	3.824%	$33.6182	$33.62	$33.60	$33.60
Purchase #4	$66.56	7.801%	$71.7523	$71.75	$71.75	$71.80
Purchase #5	$124.56	8.689%	$135.383	$135.38	$135.40	$135.40
Purchase #6	$60.75	10.840%	$67.3353	$67.34	$67.35	$67.30
Purchase #7	$79.69	11.390%	$88.7667	$88.77	$88.75	$88.80
7 purchase totals =	$455.02		$498.6718	$498.67	$498.70	$498.70