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	$109.98	9.432%	$120.3533	$120.35	$120.35	$120.40
Purchase #2	$232.44	5.799%	$245.9192	$245.92	$245.90	$245.90
Purchase #3	$59.86	11.581%	$66.7924	$66.79	$66.80	$66.80
Purchase #4	$99.49	12.464%	$111.8904	$111.89	$111.90	$111.90
Purchase #5	$213.32	7.252%	$228.79	$228.79	$228.80	$228.80
Purchase #6	$90.58	11.166%	$100.6942	$100.69	$100.70	$100.70
Purchase #7	$55.64	12.561%	$62.6289	$62.63	$62.65	$62.60
7 purchase totals =	$861.31		$937.0684	$937.06	$937.10	$937.10