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	$179.48	12.676%	$202.2309	$202.23	$202.25	$202.20
Purchase #2	$61.82	9.739%	$67.8406	$67.84	$67.85	$67.80
Purchase #3	$70.89	5.837%	$75.0278	$75.03	$75.05	$75.00
Purchase #4	$188.69	4.210%	$196.6338	$196.63	$196.65	$196.60
Purchase #5	$144.88	3.825%	$150.4217	$150.42	$150.40	$150.40
Purchase #6	$86.56	12.616%	$97.4804	$97.48	$97.50	$97.50
Purchase #7	$82.44	10.755%	$91.3064	$91.31	$91.30	$91.30
7 purchase totals =	$814.76		$880.9416	$880.94	$881.00	$880.80