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	$86.50	3.288%	$89.3441	$89.34	$89.35	$89.30
Purchase #2	$234.65	4.638%	$245.5331	$245.53	$245.55	$245.50
Purchase #3	$148.77	7.152%	$159.41	$159.41	$159.40	$159.40
Purchase #4	$102.36	12.447%	$115.1007	$115.10	$115.10	$115.10
Purchase #5	$92.45	3.688%	$95.8596	$95.86	$95.85	$95.90
Purchase #6	$23.73	6.649%	$25.3078	$25.31	$25.30	$25.30
Purchase #7	$67.37	4.480%	$70.3882	$70.39	$70.40	$70.40
7 purchase totals =	$755.83		$800.9435	$800.94	$800.95	$800.90