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	$170.25	8.573%	$184.8455	$184.85	$184.85	$184.80
Purchase #2	$245.27	6.125%	$260.2928	$260.29	$260.30	$260.30
Purchase #3	$119.68	9.125%	$130.6008	$130.60	$130.60	$130.60
Purchase #4	$167.88	3.781%	$174.2275	$174.23	$174.25	$174.20
Purchase #5	$209.31	3.113%	$215.8258	$215.83	$215.85	$215.80
Purchase #6	$196.47	13.667%	$223.3216	$223.32	$223.30	$223.30
Purchase #7	$140.59	8.304%	$152.2646	$152.26	$152.25	$152.30
7 purchase totals =	$1,249.45		$1,341.3786	$1,341.38	$1,341.40	$1,341.30