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	$90.84	6.288%	$96.552	$96.55	$96.55	$96.60
Purchase #2	$87.44	9.587%	$95.8229	$95.82	$95.80	$95.80
Purchase #3	$210.95	5.658%	$222.8856	$222.89	$222.90	$222.90
Purchase #4	$61.93	3.662%	$64.1979	$64.20	$64.20	$64.20
Purchase #5	$122.89	8.489%	$133.3221	$133.32	$133.30	$133.30
Purchase #6	$242.33	12.862%	$273.4985	$273.50	$273.50	$273.50
Purchase #7	$45.69	6.269%	$48.5543	$48.55	$48.55	$48.60
7 purchase totals =	$862.07		$934.8333	$934.83	$934.80	$934.90