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	$185.26	8.274%	$200.5884	$200.59	$200.60	$200.60
Purchase #2	$42.34	12.129%	$47.4754	$47.48	$47.50	$47.50
Purchase #3	$78.63	8.761%	$85.5188	$85.52	$85.50	$85.50
Purchase #4	$81.86	9.193%	$89.3854	$89.39	$89.40	$89.40
Purchase #5	$78.91	12.718%	$88.9458	$88.95	$88.95	$88.90
Purchase #6	$33.89	6.311%	$36.0288	$36.03	$36.05	$36.00
Purchase #7	$134.33	12.410%	$151.0004	$151.00	$151.00	$151.00
7 purchase totals =	$635.22		$698.9430	$698.96	$699.00	$698.90