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	$81.37	13.710%	$92.5258	$92.53	$92.55	$92.50
Purchase #2	$40.45	5.174%	$42.5429	$42.54	$42.55	$42.50
Purchase #3	$42.51	7.534%	$45.7127	$45.71	$45.70	$45.70
Purchase #4	$229.67	4.478%	$239.9546	$239.95	$239.95	$240.00
Purchase #5	$171.89	11.282%	$191.2826	$191.28	$191.30	$191.30
Purchase #6	$106.53	6.669%	$113.6345	$113.63	$113.65	$113.60
Purchase #7	$57.55	13.682%	$65.424	$65.42	$65.40	$65.40
7 purchase totals =	$729.97		$791.0771	$791.06	$791.10	$791.00