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	$122.93	4.676%	$128.6782	$128.68	$128.70	$128.70
Purchase #2	$63.79	13.512%	$72.4093	$72.41	$72.40	$72.40
Purchase #3	$19.80	7.241%	$21.2337	$21.23	$21.25	$21.20
Purchase #4	$209.30	7.618%	$225.2445	$225.24	$225.25	$225.20
Purchase #5	$181.69	5.620%	$191.901	$191.90	$191.90	$191.90
Purchase #6	$56.51	12.352%	$63.4901	$63.49	$63.50	$63.50
Purchase #7	$127.89	12.871%	$144.3507	$144.35	$144.35	$144.40
7 purchase totals =	$781.91		$847.3075	$847.30	$847.35	$847.30