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	$56.32	6.207%	$59.8158	$59.82	$59.80	$59.80
Purchase #2	$57.97	11.790%	$64.8047	$64.80	$64.80	$64.80
Purchase #3	$42.92	6.740%	$45.8128	$45.81	$45.80	$45.80
Purchase #4	$40.64	7.432%	$43.6604	$43.66	$43.65	$43.70
Purchase #5	$15.31	11.249%	$17.0322	$17.03	$17.05	$17.00
Purchase #6	$209.96	12.343%	$235.8754	$235.88	$235.90	$235.90
Purchase #7	$82.76	10.543%	$91.4854	$91.49	$91.50	$91.50
7 purchase totals =	$505.88		$558.4867	$558.49	$558.50	$558.50