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	$234.83	3.482%	$243.0068	$243.01	$243.00	$243.00
Purchase #2	$61.25	10.464%	$67.6592	$67.66	$67.65	$67.70
Purchase #3	$69.27	12.640%	$78.0257	$78.03	$78.05	$78.00
Purchase #4	$243.66	11.152%	$270.833	$270.83	$270.85	$270.80
Purchase #5	$119.57	9.739%	$131.2149	$131.21	$131.20	$131.20
Purchase #6	$173.97	8.695%	$189.0967	$189.10	$189.10	$189.10
Purchase #7	$160.61	12.297%	$180.3602	$180.36	$180.35	$180.40
7 purchase totals =	$1,063.16		$1,160.1965	$1,160.20	$1,160.20	$1,160.20