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	$26.81	3.546%	$27.7607	$27.76	$27.75	$27.80
Purchase #2	$210.44	3.766%	$218.3652	$218.37	$218.35	$218.40
Purchase #3	$204.70	13.144%	$231.6058	$231.61	$231.60	$231.60
Purchase #4	$212.66	10.154%	$234.2535	$234.25	$234.25	$234.30
Purchase #5	$60.84	3.356%	$62.8818	$62.88	$62.90	$62.90
Purchase #6	$56.63	4.484%	$59.1693	$59.17	$59.15	$59.20
Purchase #7	$43.80	4.689%	$45.8538	$45.85	$45.85	$45.90
7 purchase totals =	$815.88		$879.8901	$879.89	$879.85	$880.10