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	$70.50	11.441%	$78.5659	$78.57	$78.55	$78.60
Purchase #2	$216.73	8.781%	$235.7611	$235.76	$235.75	$235.80
Purchase #3	$153.81	11.705%	$171.8135	$171.81	$171.80	$171.80
Purchase #4	$168.87	3.566%	$174.8919	$174.89	$174.90	$174.90
Purchase #5	$52.97	4.461%	$55.333	$55.33	$55.35	$55.30
Purchase #6	$27.68	6.682%	$29.5296	$29.53	$29.55	$29.50
Purchase #7	$164.94	11.630%	$184.1225	$184.12	$184.10	$184.10
7 purchase totals =	$855.50		$930.0175	$930.01	$930.00	$930.00