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	$147.88	12.801%	$166.8101	$166.81	$166.80	$166.80
Purchase #2	$79.62	9.545%	$87.2197	$87.22	$87.20	$87.20
Purchase #3	$238.47	10.470%	$263.4378	$263.44	$263.45	$263.40
Purchase #4	$59.89	13.400%	$67.9153	$67.92	$67.90	$67.90
Purchase #5	$55.31	6.155%	$58.7143	$58.71	$58.70	$58.70
Purchase #6	$179.98	12.488%	$202.4559	$202.46	$202.45	$202.50
Purchase #7	$151.41	13.205%	$171.4037	$171.40	$171.40	$171.40
7 purchase totals =	$912.56		$1,017.9568	$1,017.96	$1,017.90	$1,017.90