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	$88.59	12.301%	$99.4875	$99.49	$99.50	$99.50
Purchase #2	$85.86	12.648%	$96.7196	$96.72	$96.70	$96.70
Purchase #3	$35.55	10.846%	$39.4058	$39.41	$39.40	$39.40
Purchase #4	$168.83	5.533%	$178.1714	$178.17	$178.15	$178.20
Purchase #5	$91.71	5.446%	$96.7045	$96.70	$96.70	$96.70
Purchase #6	$193.48	11.600%	$215.9237	$215.92	$215.90	$215.90
Purchase #7	$20.87	3.224%	$21.5428	$21.54	$21.55	$21.50
7 purchase totals =	$684.89		$747.9553	$747.95	$747.90	$747.90