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	$90.54	13.869%	$103.097	$103.10	$103.10	$103.10
Purchase #2	$131.28	9.586%	$143.8645	$143.86	$143.85	$143.90
Purchase #3	$89.37	11.317%	$99.484	$99.48	$99.50	$99.50
Purchase #4	$111.27	11.871%	$124.4789	$124.48	$124.50	$124.50
Purchase #5	$162.79	4.236%	$169.6858	$169.69	$169.70	$169.70
Purchase #6	$42.25	5.873%	$44.7313	$44.73	$44.75	$44.70
Purchase #7	$240.56	13.648%	$273.3916	$273.39	$273.40	$273.40
7 purchase totals =	$868.06		$958.7331	$958.73	$958.80	$958.80