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	$170.98	12.124%	$191.7096	$191.71	$191.70	$191.70
Purchase #2	$124.86	12.624%	$140.6223	$140.62	$140.60	$140.60
Purchase #3	$35.38	5.230%	$37.2304	$37.23	$37.25	$37.20
Purchase #4	$213.74	9.431%	$233.8978	$233.90	$233.90	$233.90
Purchase #5	$119.76	10.144%	$131.9085	$131.91	$131.90	$131.90
Purchase #6	$18.44	6.322%	$19.6058	$19.61	$19.60	$19.60
Purchase #7	$184.91	3.515%	$191.4096	$191.41	$191.40	$191.40
7 purchase totals =	$868.07		$946.3840	$946.39	$946.35	$946.30