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	$72.84	13.121%	$82.3973	$82.40	$82.40	$82.40
Purchase #2	$223.25	11.336%	$248.5576	$248.56	$248.55	$248.60
Purchase #3	$202.74	3.794%	$210.432	$210.43	$210.45	$210.40
Purchase #4	$148.94	7.443%	$160.0256	$160.03	$160.05	$160.00
Purchase #5	$67.77	6.259%	$72.0117	$72.01	$72.00	$72.00
Purchase #6	$159.43	3.412%	$164.8698	$164.87	$164.85	$164.90
Purchase #7	$168.60	12.581%	$189.8116	$189.81	$189.80	$189.80
7 purchase totals =	$1,043.57		$1,128.1056	$1,128.11	$1,128.10	$1,128.10