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	$92.41	6.400%	$98.3242	$98.32	$98.30	$98.30
Purchase #2	$131.52	6.860%	$140.5423	$140.54	$140.55	$140.50
Purchase #3	$56.70	4.264%	$59.1177	$59.12	$59.10	$59.10
Purchase #4	$24.98	6.829%	$26.6859	$26.69	$26.70	$26.70
Purchase #5	$38.99	9.427%	$42.6656	$42.67	$42.65	$42.70
Purchase #6	$211.82	5.251%	$222.9427	$222.94	$222.95	$222.90
Purchase #7	$196.37	12.706%	$221.3208	$221.32	$221.30	$221.30
7 purchase totals =	$752.79		$811.5992	$811.60	$811.55	$811.50