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	$36.80	13.786%	$41.8732	$41.87	$41.85	$41.90
Purchase #2	$82.34	7.388%	$88.4233	$88.42	$88.40	$88.40
Purchase #3	$115.35	4.316%	$120.3285	$120.33	$120.35	$120.30
Purchase #4	$80.59	11.279%	$89.6797	$89.68	$89.70	$89.70
Purchase #5	$227.32	13.720%	$258.5083	$258.51	$258.50	$258.50
Purchase #6	$232.77	5.850%	$246.387	$246.39	$246.40	$246.40
Purchase #7	$76.31	11.732%	$85.2627	$85.26	$85.25	$85.30
7 purchase totals =	$851.48		$930.4627	$930.46	$930.45	$930.50