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	$250.66	6.228%	$266.2711	$266.27	$266.25	$266.30
Purchase #2	$76.56	11.455%	$85.3299	$85.33	$85.35	$85.30
Purchase #3	$35.71	7.714%	$38.4647	$38.46	$38.45	$38.50
Purchase #4	$31.26	8.635%	$33.9593	$33.96	$33.95	$34.00
Purchase #5	$182.80	6.294%	$194.3054	$194.31	$194.30	$194.30
Purchase #6	$91.90	9.788%	$100.8952	$100.90	$100.90	$100.90
Purchase #7	$245.58	11.550%	$273.9445	$273.94	$273.95	$273.90
7 purchase totals =	$914.47		$993.1701	$993.17	$993.15	$993.20