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	$147.76	6.873%	$157.9155	$157.92	$157.90	$157.90
Purchase #2	$41.31	10.797%	$45.7702	$45.77	$45.75	$45.80
Purchase #3	$55.40	13.234%	$62.7316	$62.73	$62.75	$62.70
Purchase #4	$79.96	12.812%	$90.2045	$90.20	$90.20	$90.20
Purchase #5	$232.53	7.628%	$250.2674	$250.27	$250.25	$250.30
Purchase #6	$181.79	7.587%	$195.5824	$195.58	$195.60	$195.60
Purchase #7	$109.28	6.187%	$116.0412	$116.04	$116.05	$116.00
7 purchase totals =	$848.03		$918.5128	$918.51	$918.50	$918.50