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	$35.51	9.478%	$38.8756	$38.88	$38.90	$38.90
Purchase #2	$196.31	7.783%	$211.5888	$211.59	$211.60	$211.60
Purchase #3	$224.47	8.637%	$243.8575	$243.86	$243.85	$243.90
Purchase #4	$214.71	5.853%	$227.277	$227.28	$227.30	$227.30
Purchase #5	$175.42	8.666%	$190.6219	$190.62	$190.60	$190.60
Purchase #6	$124.75	3.278%	$128.8393	$128.84	$128.85	$128.80
Purchase #7	$50.73	5.676%	$53.6094	$53.61	$53.60	$53.60
7 purchase totals =	$1,021.90		$1,094.6695	$1,094.68	$1,094.70	$1,094.70