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	$121.51	5.665%	$128.3935	$128.39	$128.40	$128.40
Purchase #2	$149.71	8.350%	$162.2108	$162.21	$162.20	$162.20
Purchase #3	$80.43	10.549%	$88.9146	$88.91	$88.90	$88.90
Purchase #4	$114.46	7.616%	$123.1773	$123.18	$123.20	$123.20
Purchase #5	$211.54	3.704%	$219.3754	$219.38	$219.40	$219.40
Purchase #6	$178.67	4.386%	$186.5065	$186.51	$186.50	$186.50
Purchase #7	$64.51	4.542%	$67.44	$67.44	$67.45	$67.40
7 purchase totals =	$920.83		$976.0181	$976.02	$976.05	$976.00