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	$221.73	6.791%	$236.7877	$236.79	$236.80	$236.80
Purchase #2	$173.99	9.399%	$190.3433	$190.34	$190.35	$190.30
Purchase #3	$250.37	10.649%	$277.0319	$277.03	$277.05	$277.00
Purchase #4	$63.67	4.521%	$66.5485	$66.55	$66.55	$66.50
Purchase #5	$82.31	10.417%	$90.8842	$90.88	$90.90	$90.90
Purchase #6	$165.88	9.264%	$181.2471	$181.25	$181.25	$181.20
Purchase #7	$189.43	3.388%	$195.8479	$195.85	$195.85	$195.80
7 purchase totals =	$1,147.38		$1,238.6906	$1,238.69	$1,238.75	$1,238.50