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	$25.62	7.398%	$27.5154	$27.52	$27.50	$27.50
Purchase #2	$105.35	6.831%	$112.5465	$112.55	$112.55	$112.50
Purchase #3	$76.26	8.780%	$82.9556	$82.96	$82.95	$83.00
Purchase #4	$213.74	7.480%	$229.7278	$229.73	$229.75	$229.70
Purchase #5	$162.97	7.262%	$174.8049	$174.80	$174.80	$174.80
Purchase #6	$145.61	4.695%	$152.4464	$152.45	$152.45	$152.40
Purchase #7	$70.56	3.317%	$72.9005	$72.90	$72.90	$72.90
7 purchase totals =	$800.11		$852.8971	$852.91	$852.90	$852.80