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	$42.77	11.420%	$47.6543	$47.65	$47.65	$47.70
Purchase #2	$113.48	6.121%	$120.4261	$120.43	$120.45	$120.40
Purchase #3	$73.53	7.220%	$78.8389	$78.84	$78.85	$78.80
Purchase #4	$86.28	3.623%	$89.4059	$89.41	$89.40	$89.40
Purchase #5	$189.58	3.105%	$195.4665	$195.47	$195.45	$195.50
Purchase #6	$26.31	3.592%	$27.2551	$27.26	$27.25	$27.30
Purchase #7	$78.72	10.409%	$86.914	$86.91	$86.90	$86.90
7 purchase totals =	$610.67		$645.9608	$645.97	$645.95	$646.00