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	$87.76	13.666%	$99.7533	$99.75	$99.75	$99.80
Purchase #2	$55.29	11.240%	$61.5046	$61.50	$61.50	$61.50
Purchase #3	$160.53	8.465%	$174.1189	$174.12	$174.10	$174.10
Purchase #4	$161.76	13.847%	$184.1589	$184.16	$184.15	$184.20
Purchase #5	$43.81	7.448%	$47.073	$47.07	$47.05	$47.10
Purchase #6	$102.34	7.251%	$109.7607	$109.76	$109.75	$109.80
Purchase #7	$175.28	13.296%	$198.5852	$198.59	$198.60	$198.60
7 purchase totals =	$786.77		$874.9546	$874.95	$874.90	$875.10