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	$39.46	6.646%	$42.0825	$42.08	$42.10	$42.10
Purchase #2	$150.61	11.820%	$168.4121	$168.41	$168.40	$168.40
Purchase #3	$73.78	11.498%	$82.2632	$82.26	$82.25	$82.30
Purchase #4	$60.74	7.401%	$65.2354	$65.24	$65.25	$65.20
Purchase #5	$112.33	4.851%	$117.7791	$117.78	$117.80	$117.80
Purchase #6	$181.72	8.736%	$197.5951	$197.60	$197.60	$197.60
Purchase #7	$50.44	3.865%	$52.3895	$52.39	$52.40	$52.40
7 purchase totals =	$669.08		$725.7569	$725.76	$725.80	$725.80