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	$70.79	11.427%	$78.8792	$78.88	$78.90	$78.90
Purchase #2	$114.96	13.832%	$130.8613	$130.86	$130.85	$130.90
Purchase #3	$85.70	6.451%	$91.2285	$91.23	$91.25	$91.20
Purchase #4	$8.64	8.184%	$9.3471	$9.35	$9.35	$9.30
Purchase #5	$61.79	6.550%	$65.8372	$65.84	$65.85	$65.80
Purchase #6	$57.29	7.280%	$61.4607	$61.46	$61.45	$61.50
Purchase #7	$186.61	10.656%	$206.4952	$206.50	$206.50	$206.50
7 purchase totals =	$585.78		$644.1092	$644.12	$644.15	$644.10