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	$80.80	6.170%	$85.7854	$85.79	$85.80	$85.80
Purchase #2	$234.89	12.200%	$263.5466	$263.55	$263.55	$263.50
Purchase #3	$43.87	3.444%	$45.3809	$45.38	$45.40	$45.40
Purchase #4	$226.81	3.133%	$233.916	$233.92	$233.90	$233.90
Purchase #5	$54.85	13.443%	$62.2235	$62.22	$62.20	$62.20
Purchase #6	$182.51	11.426%	$203.3636	$203.36	$203.35	$203.40
Purchase #7	$101.61	8.193%	$109.9349	$109.93	$109.95	$109.90
7 purchase totals =	$925.34		$1,004.1509	$1,004.15	$1,004.15	$1,004.10