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	$71.71	9.511%	$78.5303	$78.53	$78.55	$78.50
Purchase #2	$64.92	3.538%	$67.2169	$67.22	$67.20	$67.20
Purchase #3	$102.32	6.759%	$109.2358	$109.24	$109.25	$109.20
Purchase #4	$65.38	12.490%	$73.546	$73.55	$73.55	$73.50
Purchase #5	$250.65	13.269%	$283.9087	$283.91	$283.90	$283.90
Purchase #6	$30.34	11.310%	$33.7715	$33.77	$33.75	$33.80
Purchase #7	$233.93	11.122%	$259.9477	$259.95	$259.95	$259.90
7 purchase totals =	$819.25		$906.1569	$906.17	$906.15	$906.00