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	$67.30	12.432%	$75.6667	$75.67	$75.65	$75.70
Purchase #2	$70.98	10.279%	$78.276	$78.28	$78.30	$78.30
Purchase #3	$64.71	12.157%	$72.5768	$72.58	$72.60	$72.60
Purchase #4	$49.57	6.557%	$52.8203	$52.82	$52.80	$52.80
Purchase #5	$96.95	7.162%	$103.8936	$103.89	$103.90	$103.90
Purchase #6	$30.84	6.263%	$32.7715	$32.77	$32.75	$32.80
Purchase #7	$120.95	6.425%	$128.721	$128.72	$128.70	$128.70
7 purchase totals =	$501.30		$544.7259	$544.73	$544.70	$544.80