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	$80.59	3.477%	$83.3921	$83.39	$83.40	$83.40
Purchase #2	$216.88	10.858%	$240.4288	$240.43	$240.45	$240.40
Purchase #3	$37.99	3.765%	$39.4203	$39.42	$39.40	$39.40
Purchase #4	$237.38	11.829%	$265.4597	$265.46	$265.45	$265.50
Purchase #5	$156.70	10.340%	$172.9028	$172.90	$172.90	$172.90
Purchase #6	$234.34	11.782%	$261.9499	$261.95	$261.95	$261.90
Purchase #7	$46.77	11.812%	$52.2945	$52.29	$52.30	$52.30
7 purchase totals =	$1,010.65		$1,115.8481	$1,115.84	$1,115.85	$1,115.80