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	$185.30	6.305%	$196.9832	$196.98	$197.00	$197.00
Purchase #2	$243.43	12.258%	$273.2696	$273.27	$273.25	$273.30
Purchase #3	$161.76	6.436%	$172.1709	$172.17	$172.15	$172.20
Purchase #4	$209.40	6.456%	$222.9189	$222.92	$222.90	$222.90
Purchase #5	$194.58	7.695%	$209.5529	$209.55	$209.55	$209.60
Purchase #6	$134.75	3.543%	$139.5242	$139.52	$139.50	$139.50
Purchase #7	$113.58	5.605%	$119.9462	$119.95	$119.95	$119.90
7 purchase totals =	$1,242.80		$1,334.3659	$1,334.36	$1,334.30	$1,334.40