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	$193.50	11.553%	$215.8551	$215.86	$215.85	$215.90
Purchase #2	$77.58	3.331%	$80.1642	$80.16	$80.15	$80.20
Purchase #3	$206.91	4.780%	$216.8003	$216.80	$216.80	$216.80
Purchase #4	$159.59	6.419%	$169.8341	$169.83	$169.85	$169.80
Purchase #5	$86.90	4.179%	$90.5316	$90.53	$90.55	$90.50
Purchase #6	$85.29	12.293%	$95.7747	$95.77	$95.75	$95.80
Purchase #7	$228.34	9.822%	$250.7676	$250.77	$250.75	$250.80
7 purchase totals =	$1,038.11		$1,119.7276	$1,119.72	$1,119.70	$1,119.80