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	$69.94	10.612%	$77.362	$77.36	$77.35	$77.40
Purchase #2	$179.76	4.192%	$187.2955	$187.30	$187.30	$187.30
Purchase #3	$44.74	11.667%	$49.9598	$49.96	$49.95	$50.00
Purchase #4	$71.52	9.754%	$78.4961	$78.50	$78.50	$78.50
Purchase #5	$116.43	10.299%	$128.4211	$128.42	$128.40	$128.40
Purchase #6	$33.52	8.571%	$36.393	$36.39	$36.40	$36.40
Purchase #7	$84.34	7.792%	$90.9118	$90.91	$90.90	$90.90
7 purchase totals =	$600.25		$648.8393	$648.84	$648.80	$648.90