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	$157.71	6.168%	$167.4376	$167.44	$167.45	$167.40
Purchase #2	$125.46	13.244%	$142.0759	$142.08	$142.10	$142.10
Purchase #3	$94.89	9.562%	$103.9634	$103.96	$103.95	$104.00
Purchase #4	$79.89	13.795%	$90.9108	$90.91	$90.90	$90.90
Purchase #5	$182.67	11.692%	$204.0278	$204.03	$204.05	$204.00
Purchase #6	$70.73	13.614%	$80.3592	$80.36	$80.35	$80.40
Purchase #7	$81.84	10.452%	$90.3939	$90.39	$90.40	$90.40
7 purchase totals =	$793.19		$879.1686	$879.17	$879.20	$879.20