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	$70.83	4.369%	$73.9246	$73.92	$73.90	$73.90
Purchase #2	$211.30	11.869%	$236.3792	$236.38	$236.40	$236.40
Purchase #3	$190.89	4.813%	$200.0775	$200.08	$200.10	$200.10
Purchase #4	$29.64	7.317%	$31.8088	$31.81	$31.80	$31.80
Purchase #5	$183.33	4.483%	$191.5487	$191.55	$191.55	$191.50
Purchase #6	$52.76	9.180%	$57.6034	$57.60	$57.60	$57.60
Purchase #7	$131.75	11.560%	$146.9803	$146.98	$147.00	$147.00
7 purchase totals =	$870.50		$938.3225	$938.32	$938.35	$938.30