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	$33.25	12.767%	$37.495	$37.50	$37.50	$37.50
Purchase #2	$95.43	9.749%	$104.7335	$104.73	$104.75	$104.70
Purchase #3	$31.88	12.568%	$35.8867	$35.89	$35.90	$35.90
Purchase #4	$161.76	3.317%	$167.1256	$167.13	$167.15	$167.10
Purchase #5	$50.90	13.648%	$57.8468	$57.85	$57.85	$57.80
Purchase #6	$116.35	6.562%	$123.9849	$123.98	$124.00	$124.00
Purchase #7	$200.52	13.590%	$227.7707	$227.77	$227.75	$227.80
7 purchase totals =	$690.09		$754.8432	$754.85	$754.90	$754.80