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	$19.48	10.312%	$21.4888	$21.49	$21.50	$21.50
Purchase #2	$224.75	3.398%	$232.387	$232.39	$232.40	$232.40
Purchase #3	$146.91	3.165%	$151.5597	$151.56	$151.55	$151.60
Purchase #4	$178.73	3.555%	$185.0839	$185.08	$185.10	$185.10
Purchase #5	$78.71	5.639%	$83.1485	$83.15	$83.15	$83.10
Purchase #6	$115.89	13.115%	$131.089	$131.09	$131.10	$131.10
Purchase #7	$159.54	5.869%	$168.9034	$168.90	$168.90	$168.90
7 purchase totals =	$924.01		$973.6603	$973.66	$973.70	$973.70