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	$136.91	4.797%	$143.4776	$143.48	$143.50	$143.50
Purchase #2	$121.36	7.568%	$130.5445	$130.54	$130.55	$130.50
Purchase #3	$118.31	4.502%	$123.6363	$123.64	$123.65	$123.60
Purchase #4	$153.38	7.290%	$164.5614	$164.56	$164.55	$164.60
Purchase #5	$149.82	12.106%	$167.9572	$167.96	$167.95	$168.00
Purchase #6	$12.42	6.781%	$13.2622	$13.26	$13.25	$13.30
Purchase #7	$181.90	3.201%	$187.7226	$187.72	$187.70	$187.70
7 purchase totals =	$874.10		$931.1618	$931.16	$931.15	$931.20