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	$132.48	5.619%	$139.9241	$139.92	$139.90	$139.90
Purchase #2	$39.33	5.115%	$41.3417	$41.34	$41.35	$41.30
Purchase #3	$55.96	11.386%	$62.3316	$62.33	$62.35	$62.30
Purchase #4	$103.59	9.104%	$113.0208	$113.02	$113.00	$113.00
Purchase #5	$219.72	11.193%	$244.3133	$244.31	$244.30	$244.30
Purchase #6	$36.40	5.517%	$38.4082	$38.41	$38.40	$38.40
Purchase #7	$6.82	8.573%	$7.4047	$7.40	$7.40	$7.40
7 purchase totals =	$594.30		$646.7444	$646.73	$646.70	$646.60