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	$66.63	7.602%	$71.6952	$71.70	$71.70	$71.70
Purchase #2	$135.70	12.435%	$152.5743	$152.57	$152.55	$152.60
Purchase #3	$215.69	5.389%	$227.3135	$227.31	$227.30	$227.30
Purchase #4	$213.44	4.436%	$222.9082	$222.91	$222.90	$222.90
Purchase #5	$129.67	3.279%	$133.9219	$133.92	$133.90	$133.90
Purchase #6	$89.28	11.587%	$99.6249	$99.62	$99.60	$99.60
Purchase #7	$142.75	11.276%	$158.8465	$158.85	$158.85	$158.80
7 purchase totals =	$993.16		$1,066.8845	$1,066.88	$1,066.80	$1,066.80