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	$50.90	12.158%	$57.0884	$57.09	$57.10	$57.10
Purchase #2	$180.96	8.707%	$196.7162	$196.72	$196.70	$196.70
Purchase #3	$242.46	11.606%	$270.5999	$270.60	$270.60	$270.60
Purchase #4	$227.26	5.832%	$240.5138	$240.51	$240.50	$240.50
Purchase #5	$205.35	10.740%	$227.4046	$227.40	$227.40	$227.40
Purchase #6	$85.93	10.601%	$95.0394	$95.04	$95.05	$95.00
Purchase #7	$90.56	3.618%	$93.8365	$93.84	$93.85	$93.80
7 purchase totals =	$1,083.42		$1,181.1988	$1,181.20	$1,181.20	$1,181.10