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	$153.61	4.277%	$160.1799	$160.18	$160.20	$160.20
Purchase #2	$25.94	6.111%	$27.5252	$27.53	$27.55	$27.50
Purchase #3	$135.27	12.705%	$152.4561	$152.46	$152.45	$152.50
Purchase #4	$62.55	12.197%	$70.1792	$70.18	$70.20	$70.20
Purchase #5	$66.43	9.543%	$72.7694	$72.77	$72.75	$72.80
Purchase #6	$139.25	3.613%	$144.2811	$144.28	$144.30	$144.30
Purchase #7	$170.60	11.270%	$189.8266	$189.83	$189.85	$189.80
7 purchase totals =	$753.65		$817.2175	$817.23	$817.30	$817.30