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	$120.98	8.645%	$131.4387	$131.44	$131.45	$131.40
Purchase #2	$196.99	3.842%	$204.5584	$204.56	$204.55	$204.60
Purchase #3	$114.41	11.662%	$127.7525	$127.75	$127.75	$127.80
Purchase #4	$155.86	3.505%	$161.3229	$161.32	$161.30	$161.30
Purchase #5	$247.59	5.331%	$260.789	$260.79	$260.80	$260.80
Purchase #6	$171.72	9.664%	$188.315	$188.32	$188.30	$188.30
Purchase #7	$54.41	5.473%	$57.3879	$57.39	$57.40	$57.40
7 purchase totals =	$1,061.96		$1,131.5644	$1,131.57	$1,131.55	$1,131.60