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	$137.70	6.752%	$146.9975	$147.00	$147.00	$147.00
Purchase #2	$168.57	12.486%	$189.6177	$189.62	$189.60	$189.60
Purchase #3	$72.97	7.574%	$78.4967	$78.50	$78.50	$78.50
Purchase #4	$32.73	3.520%	$33.8821	$33.88	$33.90	$33.90
Purchase #5	$73.82	9.159%	$80.5812	$80.58	$80.60	$80.60
Purchase #6	$212.61	8.489%	$230.6585	$230.66	$230.65	$230.70
Purchase #7	$224.53	8.418%	$243.4309	$243.43	$243.45	$243.40
7 purchase totals =	$922.93		$1,003.6646	$1,003.67	$1,003.70	$1,003.70