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	$228.46	11.790%	$255.3954	$255.40	$255.40	$255.40
Purchase #2	$162.32	6.357%	$172.6387	$172.64	$172.65	$172.60
Purchase #3	$131.74	13.303%	$149.2654	$149.27	$149.25	$149.30
Purchase #4	$250.92	11.863%	$280.6866	$280.69	$280.70	$280.70
Purchase #5	$96.78	6.442%	$103.0146	$103.01	$103.00	$103.00
Purchase #6	$43.96	7.529%	$47.2697	$47.27	$47.25	$47.30
Purchase #7	$245.55	12.655%	$276.6244	$276.62	$276.60	$276.60
7 purchase totals =	$1,159.73		$1,284.8948	$1,284.90	$1,284.85	$1,284.90