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	$45.81	12.230%	$51.4126	$51.41	$51.40	$51.40
Purchase #2	$27.74	11.524%	$30.9368	$30.94	$30.95	$30.90
Purchase #3	$250.77	5.595%	$264.8006	$264.80	$264.80	$264.80
Purchase #4	$67.65	9.247%	$73.9056	$73.91	$73.90	$73.90
Purchase #5	$74.85	9.653%	$82.0753	$82.08	$82.10	$82.10
Purchase #6	$69.44	12.859%	$78.3693	$78.37	$78.35	$78.40
Purchase #7	$224.63	7.874%	$242.3174	$242.32	$242.30	$242.30
7 purchase totals =	$760.89		$823.8176	$823.83	$823.80	$823.80