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	$179.56	6.859%	$191.876	$191.88	$191.90	$191.90
Purchase #2	$188.54	12.195%	$211.5325	$211.53	$211.55	$211.50
Purchase #3	$72.65	13.864%	$82.7222	$82.72	$82.70	$82.70
Purchase #4	$32.66	5.120%	$34.3322	$34.33	$34.35	$34.30
Purchase #5	$139.42	5.695%	$147.36	$147.36	$147.35	$147.40
Purchase #6	$85.66	12.515%	$96.3803	$96.38	$96.40	$96.40
Purchase #7	$240.83	6.515%	$256.5201	$256.52	$256.50	$256.50
7 purchase totals =	$939.32		$1,020.7233	$1,020.72	$1,020.75	$1,020.70