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	$180.66	10.756%	$200.0918	$200.09	$200.10	$200.10
Purchase #2	$25.45	13.511%	$28.8885	$28.89	$28.90	$28.90
Purchase #3	$216.98	8.588%	$235.6142	$235.61	$235.60	$235.60
Purchase #4	$89.92	4.196%	$93.693	$93.69	$93.70	$93.70
Purchase #5	$71.55	12.410%	$80.4294	$80.43	$80.45	$80.40
Purchase #6	$205.48	8.662%	$223.2787	$223.28	$223.30	$223.30
Purchase #7	$75.51	8.805%	$82.1587	$82.16	$82.15	$82.20
7 purchase totals =	$865.55		$944.1543	$944.15	$944.20	$944.20