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	$52.86	8.738%	$57.4789	$57.48	$57.50	$57.50
Purchase #2	$98.31	3.676%	$101.9239	$101.92	$101.90	$101.90
Purchase #3	$71.54	9.124%	$78.0673	$78.07	$78.05	$78.10
Purchase #4	$233.56	3.164%	$240.9498	$240.95	$240.95	$240.90
Purchase #5	$42.78	8.645%	$46.4783	$46.48	$46.50	$46.50
Purchase #6	$17.35	12.574%	$19.5316	$19.53	$19.55	$19.50
Purchase #7	$200.25	6.508%	$213.2823	$213.28	$213.30	$213.30
7 purchase totals =	$716.65		$757.7121	$757.71	$757.75	$757.70