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	$78.51	12.586%	$88.3913	$88.39	$88.40	$88.40
Purchase #2	$142.51	12.467%	$160.2767	$160.28	$160.30	$160.30
Purchase #3	$157.46	5.636%	$166.3344	$166.33	$166.35	$166.30
Purchase #4	$104.55	5.427%	$110.2239	$110.22	$110.20	$110.20
Purchase #5	$44.65	10.460%	$49.3204	$49.32	$49.30	$49.30
Purchase #6	$63.81	13.300%	$72.2967	$72.30	$72.30	$72.30
Purchase #7	$75.34	8.863%	$82.0174	$82.02	$82.00	$82.00
7 purchase totals =	$666.83		$728.8608	$728.86	$728.85	$728.80