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	$142.78	3.454%	$147.7116	$147.71	$147.70	$147.70
Purchase #2	$42.31	6.292%	$44.9721	$44.97	$44.95	$45.00
Purchase #3	$36.69	10.144%	$40.4118	$40.41	$40.40	$40.40
Purchase #4	$83.33	7.564%	$89.6331	$89.63	$89.65	$89.60
Purchase #5	$90.59	6.233%	$96.2365	$96.24	$96.25	$96.20
Purchase #6	$138.32	12.409%	$155.4841	$155.48	$155.50	$155.50
Purchase #7	$66.57	9.727%	$73.0453	$73.05	$73.05	$73.00
7 purchase totals =	$600.59		$647.4945	$647.49	$647.50	$647.40