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	$98.41	3.696%	$102.0472	$102.05	$102.05	$102.00
Purchase #2	$118.33	8.653%	$128.5691	$128.57	$128.55	$128.60
Purchase #3	$62.70	13.598%	$71.2259	$71.23	$71.25	$71.20
Purchase #4	$174.77	3.316%	$180.5654	$180.57	$180.55	$180.60
Purchase #5	$96.31	4.712%	$100.8481	$100.85	$100.85	$100.80
Purchase #6	$64.90	12.133%	$72.7743	$72.77	$72.75	$72.80
Purchase #7	$21.77	8.518%	$23.6244	$23.62	$23.60	$23.60
7 purchase totals =	$637.19		$679.6544	$679.66	$679.60	$679.60