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	$244.99	12.224%	$274.9376	$274.94	$274.95	$274.90
Purchase #2	$136.33	10.683%	$150.8941	$150.89	$150.90	$150.90
Purchase #3	$134.73	9.662%	$147.7476	$147.75	$147.75	$147.70
Purchase #4	$184.71	7.645%	$198.8311	$198.83	$198.85	$198.80
Purchase #5	$70.27	12.410%	$78.9905	$78.99	$79.00	$79.00
Purchase #6	$131.54	12.799%	$148.3758	$148.38	$148.40	$148.40
Purchase #7	$153.31	13.799%	$174.4652	$174.47	$174.45	$174.50
7 purchase totals =	$1,055.88		$1,174.2419	$1,174.25	$1,174.30	$1,174.20