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	$63.61	13.484%	$72.1872	$72.19	$72.20	$72.20
Purchase #2	$94.50	7.720%	$101.7954	$101.80	$101.80	$101.80
Purchase #3	$116.79	11.648%	$130.3937	$130.39	$130.40	$130.40
Purchase #4	$36.86	8.568%	$40.0182	$40.02	$40.00	$40.00
Purchase #5	$133.78	13.862%	$152.3246	$152.32	$152.30	$152.30
Purchase #6	$80.40	10.347%	$88.719	$88.72	$88.70	$88.70
Purchase #7	$155.70	4.115%	$162.1071	$162.11	$162.10	$162.10
7 purchase totals =	$681.64		$747.5452	$747.55	$747.50	$747.50