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	$37.99	12.669%	$42.803	$42.80	$42.80	$42.80
Purchase #2	$157.74	7.278%	$169.2203	$169.22	$169.20	$169.20
Purchase #3	$246.59	9.315%	$269.5599	$269.56	$269.55	$269.60
Purchase #4	$117.51	11.709%	$131.2692	$131.27	$131.25	$131.30
Purchase #5	$110.72	11.494%	$123.4462	$123.45	$123.45	$123.40
Purchase #6	$122.57	10.798%	$135.8051	$135.81	$135.80	$135.80
Purchase #7	$138.98	8.365%	$150.6057	$150.61	$150.60	$150.60
7 purchase totals =	$932.10		$1,022.7094	$1,022.72	$1,022.65	$1,022.70