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	$31.26	12.498%	$35.1669	$35.17	$35.15	$35.20
Purchase #2	$81.89	11.634%	$91.4171	$91.42	$91.40	$91.40
Purchase #3	$206.30	10.737%	$228.4504	$228.45	$228.45	$228.50
Purchase #4	$36.30	4.516%	$37.9393	$37.94	$37.95	$37.90
Purchase #5	$78.81	13.641%	$89.5605	$89.56	$89.55	$89.60
Purchase #6	$226.91	6.761%	$242.2514	$242.25	$242.25	$242.30
Purchase #7	$53.76	6.379%	$57.1894	$57.19	$57.20	$57.20
7 purchase totals =	$715.23		$781.9750	$781.98	$781.95	$782.10