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	$50.45	10.474%	$55.7341	$55.73	$55.75	$55.70
Purchase #2	$244.63	5.849%	$258.9384	$258.94	$258.95	$258.90
Purchase #3	$145.33	3.384%	$150.248	$150.25	$150.25	$150.20
Purchase #4	$36.74	12.804%	$41.4442	$41.44	$41.45	$41.40
Purchase #5	$38.30	11.870%	$42.8462	$42.85	$42.85	$42.80
Purchase #6	$104.27	10.567%	$115.2882	$115.29	$115.30	$115.30
Purchase #7	$140.45	11.652%	$156.8152	$156.82	$156.80	$156.80
7 purchase totals =	$760.17		$821.3143	$821.32	$821.35	$821.10