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	$116.90	12.152%	$131.1057	$131.11	$131.10	$131.10
Purchase #2	$184.73	3.394%	$190.9997	$191.00	$191.00	$191.00
Purchase #3	$186.66	13.182%	$211.2655	$211.27	$211.25	$211.30
Purchase #4	$102.25	11.502%	$114.0108	$114.01	$114.00	$114.00
Purchase #5	$64.88	13.445%	$73.6031	$73.60	$73.60	$73.60
Purchase #6	$48.38	4.303%	$50.4618	$50.46	$50.45	$50.50
Purchase #7	$125.33	12.400%	$140.8709	$140.87	$140.85	$140.90
7 purchase totals =	$829.13		$912.3175	$912.32	$912.25	$912.40