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	$71.56	8.871%	$77.9081	$77.91	$77.90	$77.90
Purchase #2	$222.54	11.485%	$248.0987	$248.10	$248.10	$248.10
Purchase #3	$208.72	12.173%	$234.1275	$234.13	$234.15	$234.10
Purchase #4	$77.32	11.722%	$86.3835	$86.38	$86.40	$86.40
Purchase #5	$33.29	5.513%	$35.1253	$35.13	$35.15	$35.10
Purchase #6	$43.90	9.761%	$48.1851	$48.19	$48.20	$48.20
Purchase #7	$73.67	11.771%	$82.3417	$82.34	$82.35	$82.30
7 purchase totals =	$731.00		$812.1699	$812.18	$812.25	$812.10