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	$7.90	3.649%	$8.1883	$8.19	$8.20	$8.20
Purchase #2	$6.78	12.560%	$7.6316	$7.63	$7.65	$7.60
Purchase #3	$161.73	4.238%	$168.5841	$168.58	$168.60	$168.60
Purchase #4	$66.32	9.150%	$72.3883	$72.39	$72.40	$72.40
Purchase #5	$79.37	11.684%	$88.6436	$88.64	$88.65	$88.60
Purchase #6	$136.78	4.179%	$142.496	$142.50	$142.50	$142.50
Purchase #7	$185.88	13.169%	$210.3585	$210.36	$210.35	$210.40
7 purchase totals =	$644.76		$698.2904	$698.29	$698.35	$698.30