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	$37.83	4.548%	$39.5505	$39.55	$39.55	$39.60
Purchase #2	$49.46	11.231%	$55.0149	$55.01	$55.00	$55.00
Purchase #3	$25.33	13.407%	$28.726	$28.73	$28.75	$28.70
Purchase #4	$68.63	6.567%	$73.1369	$73.14	$73.15	$73.10
Purchase #5	$31.48	3.794%	$32.6744	$32.67	$32.65	$32.70
Purchase #6	$162.39	11.467%	$181.0113	$181.01	$181.00	$181.00
Purchase #7	$104.45	8.455%	$113.2812	$113.28	$113.30	$113.30
7 purchase totals =	$479.57		$523.3952	$523.39	$523.40	$523.40