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	$247.38	9.450%	$270.7574	$270.76	$270.75	$270.80
Purchase #2	$215.75	8.412%	$233.8989	$233.90	$233.90	$233.90
Purchase #3	$96.73	6.488%	$103.0058	$103.01	$103.00	$103.00
Purchase #4	$131.26	4.183%	$136.7506	$136.75	$136.75	$136.80
Purchase #5	$142.36	7.254%	$152.6868	$152.69	$152.70	$152.70
Purchase #6	$130.39	4.702%	$136.5209	$136.52	$136.50	$136.50
Purchase #7	$53.46	8.251%	$57.871	$57.87	$57.85	$57.90
7 purchase totals =	$1,017.33		$1,091.4914	$1,091.50	$1,091.45	$1,091.60