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	$5.41	7.639%	$5.8233	$5.82	$5.80	$5.80
Purchase #2	$150.77	12.310%	$169.3298	$169.33	$169.35	$169.30
Purchase #3	$164.93	9.684%	$180.9018	$180.90	$180.90	$180.90
Purchase #4	$85.69	13.787%	$97.5041	$97.50	$97.50	$97.50
Purchase #5	$127.56	9.290%	$139.4103	$139.41	$139.40	$139.40
Purchase #6	$139.59	7.748%	$150.4054	$150.41	$150.40	$150.40
Purchase #7	$150.57	10.615%	$166.553	$166.55	$166.55	$166.60
7 purchase totals =	$824.52		$909.9277	$909.92	$909.90	$909.90