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	$51.51	5.499%	$54.3425	$54.34	$54.35	$54.30
Purchase #2	$155.89	8.229%	$168.7182	$168.72	$168.70	$168.70
Purchase #3	$57.37	4.179%	$59.7675	$59.77	$59.75	$59.80
Purchase #4	$222.80	6.424%	$237.1127	$237.11	$237.10	$237.10
Purchase #5	$47.50	7.736%	$51.1746	$51.17	$51.15	$51.20
Purchase #6	$126.45	6.266%	$134.3734	$134.37	$134.35	$134.40
Purchase #7	$53.99	8.323%	$58.4836	$58.48	$58.50	$58.50
7 purchase totals =	$715.51		$763.9725	$763.96	$763.90	$764.00