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	$149.86	13.660%	$170.3309	$170.33	$170.35	$170.30
Purchase #2	$79.43	5.510%	$83.8066	$83.81	$83.80	$83.80
Purchase #3	$213.59	8.474%	$231.6896	$231.69	$231.70	$231.70
Purchase #4	$223.33	3.790%	$231.7942	$231.79	$231.80	$231.80
Purchase #5	$55.65	12.234%	$62.4582	$62.46	$62.45	$62.50
Purchase #6	$182.57	11.334%	$203.2625	$203.26	$203.25	$203.30
Purchase #7	$138.33	4.488%	$144.5383	$144.54	$144.55	$144.50
7 purchase totals =	$1,042.76		$1,127.8803	$1,127.88	$1,127.90	$1,127.90