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	$31.89	12.155%	$35.7662	$35.77	$35.75	$35.80
Purchase #2	$43.56	11.435%	$48.5411	$48.54	$48.55	$48.50
Purchase #3	$150.86	9.202%	$164.7421	$164.74	$164.75	$164.70
Purchase #4	$28.64	3.312%	$29.5886	$29.59	$29.60	$29.60
Purchase #5	$27.54	7.685%	$29.6564	$29.66	$29.65	$29.70
Purchase #6	$250.41	12.584%	$281.9216	$281.92	$281.90	$281.90
Purchase #7	$148.71	13.463%	$168.7308	$168.73	$168.75	$168.70
7 purchase totals =	$681.61		$758.9468	$758.95	$758.95	$758.90