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	$55.88	3.115%	$57.6207	$57.62	$57.60	$57.60
Purchase #2	$97.80	9.134%	$106.7331	$106.73	$106.75	$106.70
Purchase #3	$95.61	11.592%	$106.6931	$106.69	$106.70	$106.70
Purchase #4	$31.36	3.366%	$32.4156	$32.42	$32.40	$32.40
Purchase #5	$116.54	12.741%	$131.3884	$131.39	$131.40	$131.40
Purchase #6	$32.41	8.314%	$35.1046	$35.10	$35.10	$35.10
Purchase #7	$233.89	11.863%	$261.6364	$261.64	$261.65	$261.60
7 purchase totals =	$663.49		$731.5919	$731.59	$731.60	$731.50