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	$77.88	6.299%	$82.7857	$82.79	$82.80	$82.80
Purchase #2	$201.73	3.809%	$209.4139	$209.41	$209.40	$209.40
Purchase #3	$240.96	9.138%	$262.9789	$262.98	$263.00	$263.00
Purchase #4	$53.61	12.555%	$60.3407	$60.34	$60.35	$60.30
Purchase #5	$167.33	8.289%	$181.2	$181.20	$181.20	$181.20
Purchase #6	$40.65	12.506%	$45.7337	$45.73	$45.75	$45.70
Purchase #7	$148.58	11.271%	$165.3265	$165.33	$165.35	$165.30
7 purchase totals =	$930.74		$1,007.7794	$1,007.78	$1,007.85	$1,007.70