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	$209.87	7.443%	$225.4906	$225.49	$225.50	$225.50
Purchase #2	$139.59	4.210%	$145.4667	$145.47	$145.45	$145.50
Purchase #3	$155.76	8.704%	$169.3174	$169.32	$169.30	$169.30
Purchase #4	$25.63	11.448%	$28.5641	$28.56	$28.55	$28.60
Purchase #5	$239.93	4.299%	$250.2446	$250.24	$250.25	$250.20
Purchase #6	$106.73	7.544%	$114.7817	$114.78	$114.80	$114.80
Purchase #7	$206.61	6.224%	$219.4694	$219.47	$219.45	$219.50
7 purchase totals =	$1,084.12		$1,153.3345	$1,153.33	$1,153.30	$1,153.40