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	$109.43	3.498%	$113.2579	$113.26	$113.25	$113.30
Purchase #2	$43.80	11.736%	$48.9404	$48.94	$48.95	$48.90
Purchase #3	$49.37	6.297%	$52.4788	$52.48	$52.50	$52.50
Purchase #4	$100.31	6.263%	$106.5924	$106.59	$106.60	$106.60
Purchase #5	$73.60	6.269%	$78.214	$78.21	$78.20	$78.20
Purchase #6	$72.91	12.597%	$82.0945	$82.09	$82.10	$82.10
Purchase #7	$84.70	12.809%	$95.5492	$95.55	$95.55	$95.50
7 purchase totals =	$534.12		$577.1272	$577.12	$577.15	$577.10