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	$42.35	13.618%	$48.1172	$48.12	$48.10	$48.10
Purchase #2	$228.83	5.492%	$241.3973	$241.40	$241.40	$241.40
Purchase #3	$42.39	5.791%	$44.8448	$44.84	$44.85	$44.80
Purchase #4	$206.34	7.556%	$221.9311	$221.93	$221.95	$221.90
Purchase #5	$170.73	13.550%	$193.8639	$193.86	$193.85	$193.90
Purchase #6	$99.26	4.560%	$103.7863	$103.79	$103.80	$103.80
Purchase #7	$71.64	10.140%	$78.9043	$78.90	$78.90	$78.90
7 purchase totals =	$861.54		$932.8449	$932.84	$932.85	$932.80