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	$38.72	5.618%	$40.8953	$40.90	$40.90	$40.90
Purchase #2	$43.30	5.804%	$45.8131	$45.81	$45.80	$45.80
Purchase #3	$26.90	5.515%	$28.3835	$28.38	$28.40	$28.40
Purchase #4	$53.95	3.540%	$55.8598	$55.86	$55.85	$55.90
Purchase #5	$93.61	9.521%	$102.5226	$102.52	$102.50	$102.50
Purchase #6	$168.95	3.309%	$174.5406	$174.54	$174.55	$174.50
Purchase #7	$148.92	4.828%	$156.1099	$156.11	$156.10	$156.10
7 purchase totals =	$574.35		$604.1248	$604.12	$604.10	$604.10