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	$12.33	4.729%	$12.9131	$12.91	$12.90	$12.90
Purchase #2	$85.79	4.498%	$89.6488	$89.65	$89.65	$89.60
Purchase #3	$81.92	8.386%	$88.7898	$88.79	$88.80	$88.80
Purchase #4	$27.58	3.179%	$28.4568	$28.46	$28.45	$28.50
Purchase #5	$28.67	13.272%	$32.4751	$32.48	$32.50	$32.50
Purchase #6	$241.53	13.375%	$273.8346	$273.83	$273.85	$273.80
Purchase #7	$73.29	5.649%	$77.4302	$77.43	$77.45	$77.40
7 purchase totals =	$551.11		$603.5484	$603.55	$603.60	$603.50