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	$113.59	6.568%	$121.0506	$121.05	$121.05	$121.10
Purchase #2	$81.42	11.725%	$90.9665	$90.97	$90.95	$91.00
Purchase #3	$72.71	7.848%	$78.4163	$78.42	$78.40	$78.40
Purchase #4	$226.43	8.397%	$245.4433	$245.44	$245.45	$245.40
Purchase #5	$226.76	13.119%	$256.5086	$256.51	$256.50	$256.50
Purchase #6	$89.97	9.185%	$98.2337	$98.23	$98.25	$98.20
Purchase #7	$160.46	13.723%	$182.4799	$182.48	$182.50	$182.50
7 purchase totals =	$971.34		$1,073.0989	$1,073.10	$1,073.10	$1,073.10