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	$93.98	6.573%	$100.1573	$100.16	$100.15	$100.20
Purchase #2	$110.69	7.269%	$118.7361	$118.74	$118.75	$118.70
Purchase #3	$193.53	12.408%	$217.5432	$217.54	$217.55	$217.50
Purchase #4	$249.81	5.577%	$263.7419	$263.74	$263.75	$263.70
Purchase #5	$101.72	9.505%	$111.3885	$111.39	$111.40	$111.40
Purchase #6	$170.82	9.367%	$186.8207	$186.82	$186.80	$186.80
Purchase #7	$152.49	7.802%	$164.3873	$164.39	$164.40	$164.40
7 purchase totals =	$1,073.04		$1,162.7750	$1,162.78	$1,162.80	$1,162.70