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	$128.67	9.767%	$141.2372	$141.24	$141.25	$141.20
Purchase #2	$39.80	6.158%	$42.2509	$42.25	$42.25	$42.30
Purchase #3	$115.47	8.593%	$125.3923	$125.39	$125.40	$125.40
Purchase #4	$94.57	9.517%	$103.5702	$103.57	$103.55	$103.60
Purchase #5	$47.46	10.316%	$52.356	$52.36	$52.35	$52.40
Purchase #6	$134.47	8.121%	$145.3903	$145.39	$145.40	$145.40
Purchase #7	$83.84	7.215%	$89.8891	$89.89	$89.90	$89.90
7 purchase totals =	$644.28		$700.0860	$700.09	$700.10	$700.20