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	$174.69	8.214%	$189.039	$189.04	$189.05	$189.00
Purchase #2	$70.45	11.402%	$78.4827	$78.48	$78.50	$78.50
Purchase #3	$136.35	3.842%	$141.5886	$141.59	$141.60	$141.60
Purchase #4	$108.32	10.581%	$119.7813	$119.78	$119.80	$119.80
Purchase #5	$225.91	8.551%	$245.2276	$245.23	$245.25	$245.20
Purchase #6	$171.34	5.211%	$180.2685	$180.27	$180.25	$180.30
Purchase #7	$24.56	9.765%	$26.9583	$26.96	$26.95	$27.00
7 purchase totals =	$911.62		$981.3460	$981.35	$981.40	$981.40