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	$153.91	9.375%	$168.3391	$168.34	$168.35	$168.30
Purchase #2	$37.71	12.482%	$42.417	$42.42	$42.40	$42.40
Purchase #3	$53.44	11.363%	$59.5124	$59.51	$59.50	$59.50
Purchase #4	$212.85	8.811%	$231.6042	$231.60	$231.60	$231.60
Purchase #5	$10.27	11.185%	$11.4187	$11.42	$11.40	$11.40
Purchase #6	$223.34	7.796%	$240.7516	$240.75	$240.75	$240.80
Purchase #7	$238.79	9.632%	$261.7903	$261.79	$261.80	$261.80
7 purchase totals =	$930.31		$1,015.8333	$1,015.83	$1,015.80	$1,015.80