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	$32.42	4.192%	$33.779	$33.78	$33.80	$33.80
Purchase #2	$53.34	4.506%	$55.7435	$55.74	$55.75	$55.70
Purchase #3	$248.89	12.593%	$280.2327	$280.23	$280.25	$280.20
Purchase #4	$179.33	9.626%	$196.5923	$196.59	$196.60	$196.60
Purchase #5	$223.61	11.406%	$249.115	$249.12	$249.10	$249.10
Purchase #6	$60.57	5.545%	$63.9286	$63.93	$63.95	$63.90
Purchase #7	$150.44	6.228%	$159.8094	$159.81	$159.80	$159.80
7 purchase totals =	$948.60		$1,039.2005	$1,039.20	$1,039.25	$1,039.10