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	$70.76	11.280%	$78.7417	$78.74	$78.75	$78.70
Purchase #2	$66.69	3.209%	$68.8301	$68.83	$68.85	$68.80
Purchase #3	$245.96	3.206%	$253.8455	$253.85	$253.85	$253.80
Purchase #4	$57.89	7.637%	$62.3111	$62.31	$62.30	$62.30
Purchase #5	$160.80	4.824%	$168.557	$168.56	$168.55	$168.60
Purchase #6	$136.35	11.272%	$151.7194	$151.72	$151.70	$151.70
Purchase #7	$116.86	7.306%	$125.3978	$125.40	$125.40	$125.40
7 purchase totals =	$855.31		$909.4026	$909.41	$909.40	$909.30