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	$133.55	10.459%	$147.518	$147.52	$147.50	$147.50
Purchase #2	$126.61	3.757%	$131.3667	$131.37	$131.35	$131.40
Purchase #3	$150.61	13.248%	$170.5628	$170.56	$170.55	$170.60
Purchase #4	$139.29	13.309%	$157.8281	$157.83	$157.85	$157.80
Purchase #5	$96.44	13.817%	$109.7651	$109.77	$109.75	$109.80
Purchase #6	$195.26	10.787%	$216.3227	$216.32	$216.30	$216.30
Purchase #7	$49.35	8.466%	$53.528	$53.53	$53.55	$53.50
7 purchase totals =	$891.11		$986.8914	$986.90	$986.85	$986.90