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	$81.31	9.308%	$88.8783	$88.88	$88.90	$88.90
Purchase #2	$56.65	4.765%	$59.3494	$59.35	$59.35	$59.30
Purchase #3	$34.96	10.131%	$38.5018	$38.50	$38.50	$38.50
Purchase #4	$116.98	4.598%	$122.3587	$122.36	$122.35	$122.40
Purchase #5	$186.44	3.664%	$193.2712	$193.27	$193.25	$193.30
Purchase #6	$95.81	3.274%	$98.9468	$98.95	$98.95	$98.90
Purchase #7	$65.83	9.377%	$72.0029	$72.00	$72.00	$72.00
7 purchase totals =	$637.98		$673.3091	$673.31	$673.30	$673.30