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	$131.90	9.310%	$144.1799	$144.18	$144.20	$144.20
Purchase #2	$142.28	3.184%	$146.8102	$146.81	$146.80	$146.80
Purchase #3	$29.91	4.144%	$31.1495	$31.15	$31.15	$31.10
Purchase #4	$22.89	13.294%	$25.933	$25.93	$25.95	$25.90
Purchase #5	$64.59	3.740%	$67.0057	$67.01	$67.00	$67.00
Purchase #6	$53.43	6.759%	$57.0413	$57.04	$57.05	$57.00
Purchase #7	$39.87	9.439%	$43.6333	$43.63	$43.65	$43.60
7 purchase totals =	$484.87		$515.7529	$515.75	$515.80	$515.60