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	$136.47	7.379%	$146.5401	$146.54	$146.55	$146.50
Purchase #2	$29.63	5.585%	$31.2848	$31.28	$31.30	$31.30
Purchase #3	$160.26	9.531%	$175.5344	$175.53	$175.55	$175.50
Purchase #4	$89.82	6.134%	$95.3296	$95.33	$95.35	$95.30
Purchase #5	$179.81	4.814%	$188.4661	$188.47	$188.45	$188.50
Purchase #6	$40.72	7.627%	$43.8257	$43.83	$43.85	$43.80
Purchase #7	$8.55	3.113%	$8.8162	$8.82	$8.80	$8.80
7 purchase totals =	$645.26		$689.7969	$689.80	$689.85	$689.70