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	$95.38	5.138%	$100.2806	$100.28	$100.30	$100.30
Purchase #2	$243.47	11.165%	$270.6534	$270.65	$270.65	$270.70
Purchase #3	$72.56	8.386%	$78.6449	$78.64	$78.65	$78.60
Purchase #4	$210.88	11.223%	$234.5471	$234.55	$234.55	$234.50
Purchase #5	$62.54	11.369%	$69.6502	$69.65	$69.65	$69.70
Purchase #6	$43.35	5.765%	$45.8491	$45.85	$45.85	$45.80
Purchase #7	$99.88	7.633%	$107.5038	$107.50	$107.50	$107.50
7 purchase totals =	$828.06		$907.1291	$907.12	$907.15	$907.10