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	$174.96	7.718%	$188.4634	$188.46	$188.45	$188.50
Purchase #2	$126.80	10.650%	$140.3042	$140.30	$140.30	$140.30
Purchase #3	$67.96	5.681%	$71.8208	$71.82	$71.80	$71.80
Purchase #4	$237.61	13.167%	$268.8961	$268.90	$268.90	$268.90
Purchase #5	$40.98	5.119%	$43.0778	$43.08	$43.10	$43.10
Purchase #6	$233.93	12.147%	$262.3455	$262.35	$262.35	$262.30
Purchase #7	$220.36	9.310%	$240.8755	$240.88	$240.90	$240.90
7 purchase totals =	$1,102.60		$1,215.7833	$1,215.79	$1,215.80	$1,215.80