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	$71.44	3.352%	$73.8347	$73.83	$73.85	$73.80
Purchase #2	$39.97	6.543%	$42.5852	$42.59	$42.60	$42.60
Purchase #3	$82.51	3.529%	$85.4218	$85.42	$85.40	$85.40
Purchase #4	$169.73	11.271%	$188.8603	$188.86	$188.85	$188.90
Purchase #5	$55.76	3.409%	$57.6609	$57.66	$57.65	$57.70
Purchase #6	$94.50	10.558%	$104.4773	$104.48	$104.50	$104.50
Purchase #7	$47.59	5.290%	$50.1075	$50.11	$50.10	$50.10
7 purchase totals =	$561.50		$602.9477	$602.95	$602.95	$603.00