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	$250.82	9.591%	$274.8761	$274.88	$274.90	$274.90
Purchase #2	$43.39	3.395%	$44.8631	$44.86	$44.85	$44.90
Purchase #3	$155.45	3.591%	$161.0322	$161.03	$161.05	$161.00
Purchase #4	$73.72	8.607%	$80.0651	$80.07	$80.05	$80.10
Purchase #5	$189.90	3.387%	$196.3319	$196.33	$196.35	$196.30
Purchase #6	$39.56	4.640%	$41.3956	$41.40	$41.40	$41.40
Purchase #7	$225.34	8.669%	$244.8747	$244.87	$244.85	$244.90
7 purchase totals =	$978.18		$1,043.4387	$1,043.44	$1,043.45	$1,043.50